Use of high tensile bolts. ( RCR40 )

Hello ,

Please could someone tell me if all or any of these bolts should be grade 8 ?

Particularly the hub bearing mounting bolts (1) , at present these are 304 stainless passenger side & grade 8 at the driver's side, so probably swapped a hub bearing at some point and used the stainless bolts.

The others are -

Caliper mounting bolts (12) - grade 8 .
Lower ball joint bolts (2) - grade 8 .
Bottom coil mounting bolts (3) - grade 8 .
Lower anti roll bar link (5) - grade 8 .

All these are 304 stainless steel -

Lower wishbones to anti roll bar link brackets (4) .
Upper anti roll bar link (6) .
Top coil bolt (7) .
Both upper (8) - & lower wishbone mountings .
Pinch bolt ( 10 ) .

Caliper mounting brackets (11) unknown - zinc plated with YFS on head.
Track rod end (9) is grade 12.9 (metric) allen bolt.

Is there anything I should be worried about ?

regards,
Ed.

I wouldn't have any stainless bolts in the suspension unless they are some of the exotic allows and the one with yes that is only grade 2.

Here is a good schematic over bolt strength, metric as well.
https://www.fastenermart.com/understanding-fastener-grades-and-classes.html

Ed;

I recommend a book "Carroll Smith's NUTS, BOLTS, FASTENERS and PLUMBING Handbook". It is a valuable reference book that you will find very useful.

As Rod pointed out, common stainless bolts are generally inferior to steel alloy bolts in strength. When I can find them, I use stainless alloy A286 fasteners. These are in the class of "Super Alloys", and are common in aerospace applications. Military & aerospace bolt specifications are strict and there is a paper trail of inspections, so their quality control is far better than generic "Grade 8" fasteners. Tensile strength is only one consideration when selecting bolts; one specification rarely mentioned in the commercial market is fatigue strength. Shear strength is another important consideration. Smith's book addresses these factors. Titanium bolts are also desirable if they are aerospace spec., usually 6Al4V.

Once in a while you can find aerospace and military hardware on eBay but be careful about their length. These bolts are not threaded all the way up their shank (that would reduce their shear strength) so they are specified as to their "grip length"- the thickness of the material being bolted, not the full length.

Commercial "high quality" fasteners are widely advertised, but be wary. I bought some ARP high strength nuts for a racing application and I was dismayed to find one nut that was unthreaded! So much for their vaunted "quality control".

Thanks for the replies.

From what I can make out, 304 stainless steel are not even up to Grade 5 spec.
Most people say never use them on suspension components.
I don't want to change them all if it isn't necessary but on the other hand I don't want any wheels or bits falling off either while driving.
Someone probably thought stainless on the undercarriage won't rust - use them instead.

regards,
Ed.

Ed - go through everything and replace with grade 8+ steel bolts from a source you trust. Get the Zinc plated variety for areas that will be exposed to water or condensation (or get it everywhere you can). Stainless should only be used for attaching hardware, wiring, and other non-load bearing items. If it’s anything greater than 1/4” I would almost always assume it should be grade 8 steel or better.

Thanks,
I've been looking at the yellow zinc plated type.
The sizes in the photos range from 3/8" for the hub bearing bolts , to 5/8" for the lower wishbone mounting bolts.
So would you not risk driving it on the road at all with stainless bolts in these places ?
I have also noticed a few other places too , roll cage mountings and I think the four trailing rods for the rear suspension.
Probably plenty of others too.

Ed;

There are plenty of counterfeit Chinese bolts out there, including "Grade 8". Be careful where you buy commercial bolts.

Ed - I wouldn’t personally risk driving the car with those bolts in place. The yellow zinc plated type would be fine. I would recommend going to steel for roll cage and all suspension points.

Does anyone use AN aircraft hardware? Pricey, but you know exactly what you are getting.

Chuck;

Check my Monday post.

CESLAW said:

Does anyone use AN aircraft hardware? Pricey, but you know exactly what you are getting.

Click to expand...

If you've got deep pockets then I don't see why not - I for one am not willing to pay the added premium for regulated and documented bolts when I can be 99.99% sure I'm getting what I need from sourcing my stuff from respectable companies. Keep in mind - almost zero of these bolt cases uses much of the bolt's actual strength/capability. I'd be willing to bet that very few bolt locations on these cars is analyzed to the degree you'd find in "standard" engineering practice. It's far faster and cheaper to overdesign these than to run FEA and load calcs on everything.

Keep in mind - stronger is not necessarily better. Going to the very high strength exotic alloys such as inconel could be a recipe for disaster with the increase in brittleness these high strength materials give you. I'd rather have a gradual versus sudden failure in just about every case, just not worth the added risk for the increase in performance.

Neil - in what instances did you consider A286 as a preferred option over standard alloy steel? The tradeoff generally isn't all that great for most applications unless you need the high temperature corrosion capabilities of A286 - not much of an issue for most of our cars.

I would caution most people away from titanium fasteners - they're especially prone to galling and there's really no need for it. An ounce or two of weight savings at very high monetary penalty with increased usage constraints ... we're not building things meant to go into space here.

I have a background in designing cryogenic and hot gas combustion devices and commonly used A286, inconel, and other super alloy exotic materials for fasteners - generally, the stronger the material, the more I hated using it for the reasons cited above. Even if cost were not an issue for me I'd tend to stick with alloy steel over the more exotic stuff, certainly in the case of our cars.

Cam;

I like A286 fasteners because they are a non- rusting "stainless" alloy but have far higher strength than 303/304 stainless. Plus the fact that some MS/NAS bolts are found on the surplus market if you look long enough. Quite a few of the bolts in my car are A286; most of my structural rivets are CherryMAX & CherryLock A286 as well- or Monel.

Normally, titanium fasteners are subject to galling (so is 303/304 stainless) but, unlike commercial titanium bolts, the aerospace fasteners are coated with anti-galling material. The USAF & NASA would not use bolts that are subject to severe galling problems. I use quite a few NAS titanium bolts, mainly in my suspension. There lightweight and non-rusting properties are advantageous.

The only Inconel I used is in the lower section of my firewall- Inconel 718. I used it because I had purchased some from a local surplus dealer and it offered excellent fire resistance, even in relatively thin sheets.

A few years ago, it was not hard to find aerospace fasteners (and other nice stuff) on the surplus market- even on eBay- at bargain prices. People simply did not know what the stuff was so there was little demand and prices were low. Many times the fasteners were cheaper that an SAE Grade 8 or even 5! Over the years, people have wised up and there are not so many opportunities to score valuable hardware at affordable prices.

Readily available AN bolts are an excellent choice as well- and readilly available from sources such as Aircraft Spruce. They offer a good combination of strength, toughness, and cost. Their quality control is light years ahead of commercial bolts.

It's an interesting take on A286; but I'm not sure the trade between A286 and 303/304 makes a lot of sense to me. Anything I've got bolted down in my car using stainless is a non-structural member and doesn't require high strength. In fact, I'm not sure I've got anything bigger than 1/4" stainless fasteners anywhere on my car. For structural bolts I'm using alloy steel usually with a tensile strength of 170ksi. A286 is available in a fairly wide range of strength depending on how it was heat treated. If memory serves, we upgraded to inconel for anything needing ~180ksi or higher strength, going even further depending on application requirements. Regardless, if you're throwing A286 at a 303/304 application then good on'ya - especially if you were able to source these fasteners on the secondary market. As you say though, are you sure the A286 you got was, indeed, "the good stuff" and not knock-offs? I pretty much assume just about everything on eBay is counterfeit or on the secondary market for some other reason. For builders who have deep pockets and aren't able to take advantage of the previously low pricing on A286, I'm still not sure it makes sense anywhere on these cars to run A286 in lieu of 303/304 or even alloy steel for that matter. I suppose if you want the pimp factor of saying you've got A286.

I've used billet Monel 400 for cryogenic applications which require high oxidation resistance. But my experience with Monel 400 is that it's really not that strong - certainly not for a bolt application. I'm not sure what kind of loads your rivets are seeing but I imagine with enough rivets you can use aluminum and still be good to go.

"The USAF & NASA would not use bolts that are subject to severe galling problems" - I'm not sure how you qualify that without defining what "severe galling" is, and without knowing what kind of installations and assembly prep have taken place. Seems like a blanket statement based on "surely they wouldn't do THAT!" unless you've got first-hand knowledge you can't let on about. Based on my own first-hand knowledge I can guarantee to you that the USAF and NASA practice very different PM schedules than the automotive field and that they are willing to trade assembly difficulties for performance whereas in automotive the trade favors maintenance and cost much moreso than performance (racing applications not included).

If you've got a PM schedule planned for your suspension I wish you luck with the R&R of those titanium bolts! Hopefully you purchased a good amount back in the day so you can swap them out without too much of a financial hit. For a builder such as myself, I'm sticking with the alloy steel stuff that's "cheap" - actually, I don't think they're cheap at all but they're affordable enough I can toss them without thinking twice about PM.

Going back to our particular application - builders working on their own cars at home - the use of titanium bolts also doesn't make much sense to me. The high cost and assembly related issues don't make the few grams of weight savings worthwhile. I've never used titanium bolts on anything I've designed but I just pulled the material properties from a titanium bolt available on McMaster - a primary source for builders - and they advertise 50ksi tensile strength for a 1/2" bolt (PN 95435A965) at $35/bolt. The equivalent bolt in alloy steel with a tensile strength of 170ksi is available for $9/pack of 5 (PN 90128A724). I'm not sure what an aerospace quality 1/2"x3" bolt goes for and what material properties you can expect - perhaps you can shed some light on that and maybe the reasoning may be clearer to me.

I'm not very good at navigating the aircraft spruce website but what's the equivalent 1/2"-13 x 3" bolt go for and what is the material strength? I tried searching but didn't come up with much on my end. Here's the closest I could find:

https://www.aircraftspruce.com/catalog/hapages/an8.php

But these bolts are advertised at 125ksi - lower strength + higher cost + stricter quality control still doesn't beat the McMaster equivalent. I've been on the receiving end of quality spills by aerospace manufacturers and maybe don't put quite as much weight on documentation as others may.

I don't have my NAS guides handy so it would take me forever to try and find an NAS bolt that would be an equivalent to the above but I'm not sure that's important.

What's my point? My point is that for an application such as ours, if you're the typical builder and don't have super deep pockets and don't have access to a horde of cheap aerospace fasteners, and don't want to read up and study all there is to know about fasteners, it makes a whole lot more sense to stick with alloy steel for structural fasteners and stainless for anything non-structural - holy long sentence Batman!

If you've got stainless at a structural location (as OP does) change it out!

Cam;

There are far fewer counterfeit aerospace fasteners than commercial ones; the economics of volume production makes it more profitable to flood hardware stores with counterfeit bolts than try to fool aerospace manufacturers with fakes. Many of the surplus bolts that I've purchased even arrived in their original BAC (Boeing) packaging so I don't question their authenticity.

As far as strength is concerned, the A286 bolts that I've used are specified as having a minimum UTS of 160,000 psi. The Monel rivets that I've used are Cherrylock or CherryMAX with Monel sleeves and Inconel 600 stems, rated as 75,000 psi ultimate shear strength. The others have a sleeve of Inconel 600 and A286 stems, also 75,000 psi. These develop high strength in 7075-T6 aluminum stressed panels.

The AN bolts on that Aircraft Spruce web page are 125,000 psi UTS minimum. A typical 1/2-20 AN8 bolt costs about $3.50 on that website. They are a good general purpose alloy steel bolt. A good high strength commercial bolt is the SPS "Unbrako" socket head cap screw but they are only black oxide coated so they eventually rust. BTW, a 1/2-13 bolt would not be a common aerospace item, those are fine thread (1/2-20); coarse thread bolts (1/2-13) is usually reserved for "engine bolt" applications such as threads in aluminum or magnesium.

As far as worrying about titanium bolts galling, NAS bolts are passivated and I use prevailing torque locknuts that have a dry lubrication coating so I've never had a problem even though I've assembled and disassembled things many, many times while it was under construction.

I'm not advocating going out and buying lots of $$$ fasteners to replace whatever a kit car manufacturer provided but if you can find them at a bargain price, why not? I don't think we disagree, Cam.

Actually Neil - I think we disagree in how information is being presented. Let me address this point before moving onto your most recent post.

OP came on here asking if he thought it was OK to use stainless fasteners in the locations he's found on his car - I think we can all universally agree that this would be a bad idea and recommend that he swap them out. It's clear to me that OP is not well versed in material science or fastener technology. You recommend that he buy Smith's book (great) but then you go on to talk about aerospace fasteners and A286 and titanium and how these fasteners can occasionally be found on eBay for a good price. You also take a jab at "commercial" fasteners and how they lack quality control, citing your experience with ARP as an example.

Here's where I have issues:
- I don't think there are any places on our cars (typically) that require A286. Referencing A286 and saying this is what you use whenever you can would lead a novice to believe that maybe they should do the same. I think A286 is a poor material selection in just about every case I can think of on my car - yours may be different. The only reason A286 should be used (in my experience) is in cases where high oxidation resistance is required and at elevated temperatures. In every location I can think of (on my car) a standard stainless fastener or zinc plated alloy steel would do the job just fine.
- I don't think there's any place for a titanium fastener (on my car). The cost and added difficulties with installation and risk of galling are too high (for me). Based on what I can gather from your posts, you prioritize oxidation resistance (and maybe weight?) over most other factors - ease of use, availability, cost. I think most other builders - though I'm going out on a limb here - would prioritize ease of use, availability, cost, weight, and oxidation resistance a little differently. My priority list differs based on application/fastener location. But in all cases I would never personally use titanium. Difference in philosophy here, but again - presented to a novice who's not familiar with materials and fasteners, I think suggesting titanium fasteners is a bad idea without also discussing the other factors in the same breath. Your 1 sentence reference to titanium fasteners doesn't do this and to someone unfamiliar with the subject they wouldn't know to go digging deeper into the rabbit hole.
- Suggesting purchasing fasteners on eBay strikes me as a bad idea. Counterfeit bolts are much more likely to be found here, even if they're bagged and tagged with labels that LOOK like a big aerospace company. Heck, it's not all that difficult to fake sheets of paper with numbers on them either. Have you seen some of the commercial goods counterfeited on eBay? You can put a pair of real and fake Beats headphones side by side and you'd never be able to tell the difference between the two without cracking them open and examining the circuit boards. Exterior packaging, instructions, everything is just about perfect these days. I've routinely reviewed material certs and it would be far easier for me to make something up on my home PC than to print out a perfect copy of the Beats headphone packaging.
- ALL manufacturers make mistakes. That you received 1 bad unit in how many millions of pieces of hardware out there isn't enough to make a catch-all statement about "commercial" manufacturers. As I've said, I've been on the receiving end of quality spills from aerospace manufacturers and I'll bet this happens much more frequently than you think they do - unless you have a background that I'm not familiar with. Why else do you think aerospace companies have whole fleets of Quality Engineers double checking everything that comes through their doors? I've personally spent 7 years as an automotive engineer and another 7 as an aerospace engineer and I've been witness to just about the entire spectrum of good and bad vendors, foreign and domestic. There are 0 companies out there who can say they've never let a non-conforming part go out the door. Getting back to the topic - for the purposes of our cars, there is absolutely nothing wrong with sourcing your fasteners from a trusted source - this has been covered many times. eBay is not a trusted source. McMaster, Fastenal, and Aircraft Spruce are examples of a trusted source. You can bet McMaster isn't sourcing their stuff from vendors on eBay or Alibaba. Since the deluge of aerospace fasteners at cheap prices is no longer available that option doesn't exist to the rest of us. I'm not going to spend 2 hours searching the internet for a good price on an aerospace spec 1/4" bolt when I can purchase a commercial 1/4" bolt from McMaster in 1 minute. Heck, I wouldn't even know where to start to find a bargain on aerospace grade fasteners.

So the reasons above are why I took issue with your post from Monday, which you referenced when Chuck came on asking about AN aircraft hardware. If Chuck wants to do the due diligence of verifying the material strength is up to snuff for his application, then that's on him - but I think it needs to be made clear that simply purchasing AN aircraft hardware doesn't mean it's superior to stuff from McMaster - just because they're a "commercial" vendor.

Your latest post:

I can't speak to the number of counterfeit fasteners, where they are prevalent, and how to identify them. I believe you're making some assumptions here though I would tend to agree that your local mom & pop hardware store is more likely to have a counterfeit fastener than McMaster or Aircraft Spruce. Yep, don't buy stuff from there, go to a trusted source for your fasteners. Again, no one is suggesting that anyone purchase fasteners from an untrusted source.

I don't know what kind of car you're building and I don't know whether your panels need to be stressed members or not. The only other car I've studied in some detail is the GTM which does have a TON of riveted panels. I don't know whether these panels are stressed members or not, however. It's great that you know what the strength of your rivets is, but do you know what percentage of that strength is required? How do you know how many rivets you need along what panels and at what spacing? Did you run FEA, do some hand calcs ... something with numbers? Whatever analysis you've done, it sounds like you're comfortable with what you're doing - great. I don't personally think 75ksi is all that strong (18-8 stainless fasteners from McMaster have a minimum of 70ksi and I put these in the category of low strength, non-structural use only). But again, you are familiar with how you're using your rivets. My personal experience with Monel is it's not very strong (and I'm comparing it to steel here since we're talking about fasteners). The ONLY reason to use Monel on my applications was for it's strength at cryogenic temperatures and fantastic oxidation resistance - neither of which are all that realistic on my car.

In the case of the AN8 fastener you've referenced on Aircraft Spruce at $3.50 per bolt and 125ksi (min) or the black oxide coated equivalent in alloy steel, would you take either of those two over the zinc coated alloy steel bolt available on McMaster at $1.80/bolt and rated at 170ksi (min)? I'd take the McMaster bolt - stronger, cheaper, and corrosion resistant, especially say in a suspension member. For the fastener novice who doesn't want to do the calculation to figure out whether 125ksi is enough, I think we can agree that they should go with the 170ksi bolt available on McMaster even though it doesn't come with a material cert. I pulled the 1/2" bolt out as a random example but thanks for letting me know about what's commonly used in aerospace with respect to TPI.

OMG - I exceeded the 10k character limit! More on the next post ...

Going back to titanium - you seem to be comfortable with how you're using the material and you're taking precautions - great. But you didn't mention this when you first brought up titanium and I think it's incumbent upon us, if we're making recommendations, to give the appropriate background risks (if they exist), especially if we know what those risks are. And here, I really believe there are risks. I would never use titanium fasteners for a suspension joint - too much risk for me. Again, you seem to know your stuff and you're happy with what you're doing. For someone who doesn't understand the risks I think it's on you to give the full story if you're going to throw that out there. I personally don't have a clue what loads were factored in when my suspension was designed and whether any off-nominal use cases were factored in, such as curbing a wheel at 20G. I'm going to use the strongest bolt I can get (within reason) and for me, that's the alloy steel bolts offered by McMaster just about every time, having considered all the cost, quality, availability, etc implications. Again, your priorities probably differ from mine. Just throwing this out, but I'm guessing most other builders will tend to be closer to my list of priorities and have less subject matter knowledge (or care to run down the rabbit hole).

I haven't done the research to see what's available with respect to pricing for A286, Monel, or titanium aerospace spec and sourced fasteners so you've got me there. I have no idea how they truly compare cost-wise to what's available from places like McMaster and Fastenal. You didn't originally mention that you were able to source your fasteners several years ago when these were on the cheap; but you did suggest going onto eBay to find some with the only caveat being to watch the grip length. Nothing about what steps one should take to ensure what's being sourced on eBay is legitimate stuff - should we contact the seller and review their certs before bidding? How do we verify that their certs are legitimate and not printed on someone's personal computer? What chemistry bounds should we be referencing when verifying a lot is metallurgically correct, and that the correct heat treat was used. In your reference to A286 you don't mention what heat treats should be sought after and which should be avoided.

Here are 2 sources for A286 fasteners, both seemingly legit (I just did a search for A286 bolts and picked the first 2):

Delta fastener

Extreme fastener

If I were someone who didn't know anything other than it's a good idea to use A286 whenever I can, which of these companies and which spec should I purchase? Someone not well versed at reviewing this type of information may not know and decide to go with the lower grade material, I mean - it's A286 right? So ... should I use a 130ksi A286 bolt which has great oxidation resistance at 1300F, or should I use a zinc plated alloy steel bolt rated to 170ksi for my upper control arm attachment point? The safest solution in this case, and probably in 99% of other searches regarding "which bolt should I use for my suspension", is to go with the 170ksi commonly available alloy steel bolt - no further explanation or rabbit hole digging needed.

Fundamentally, I don't think we disagree Neil - we should use the best stuff we can afford. Our philosophy on what makes a good design perhaps differs since our priorities aren't in alignment - and that's alright.

But take a step back and put yourself in the shoes of a novice builder looking for information on what bolts he should use for his car. Do you believe suggesting A286, titanium, and Monel fasteners is a good idea without also including all the other factors (risks, cost, availability, material strength differences)? Someone coming along a few months from now and who digs this post up and sees that you're making those recommendations may not know to dig into the rabbit hole to figure all this stuff out. So I think it's on us as subject matter experts (and I use that term very loosely in reference to myself) that we provide the appropriate background information - especially if we're going to make recommendations that carry significant risks (IMHO, you may not believe those risks exist and that's why you didn't feel it necessary to include all this extra "stuff").

You have very pretty bolts. It's a whole 'other loaded discussion on why one would choose to use a 12-point head over a 6 point head and male vs female hex. While I appreciate your anecdotes and experiences I think you should also pepper your posts with the appropriate background info if you're going to make recommendations to pursue non-traditional design options - I include the use of A286, titanium, and Monel fasteners over grade 8+ alloy steel as a non-traditional design choice. At least, I assumed you were recommending the use of A286 whenever possible since you threw it out there.

(phew, end!)

I realized just now that I didn't talk about the tribological properties of Titanium that make me not want to use it in my suspension. Untreated/uncoated titanium has poor wear properties - I think we can agree on that. I didn't purchase the paper but I'll pull this sentence from the abstract:

"However, titanium and its alloys are characterised by poor tribological behaviour in terms of high and unstable friction, severe adhesive wear, low resistance to abrasion, susceptibility to fretting wear and a strong tendency to seize."

From this article.

There's a whole field of study devoted to improving Titanium wear properties and they usually point to some type of metallurgical surface treatment (not dry film lubricant).

I believe you have some type of dry lubricant applied to your fasteners and you feel this is sufficient for whatever life cycle and usage you plan for your suspension. Do you have an estimate (thousands of miles, # of track days, or hours) before cycling them out or refreshing the lubricant? For myself, and I think the average builder, I'd be very afraid of seizing my stainless heim joint against my dry film coated titanium bolt. I'm personally much more confident about adding grease or Moly (available as a dry film spray) to my steel on steel suspension joints than to risk titanium.

Throw in cost, available, strength factors, and it just doesn't add up as the most optimized design solution for me.

Apologies for the essay - I'm waiting for guests to come by the house so I'm twiddling my thumbs a bit until they show up!

Just going back to the OP's question - ditto what's been said.....don't use stainless hardware in the suspension. Stainless is fine where it's not bearing a significant load, and can be helpful in those places particularly in a corrosive environment.

Good quality grade 8 from a reputable source is a good choice for suspension. I tend to use McMaster and Grainger for good quality hardware.

As has been said, best to get the zinc coated rather than raw as raw will rust quickly. There's different levels of zinc coating too....generally the heavier the coating the more corrosion resistance. In metric, use 12.9 for suspension over 8.8 or 10.9. Where bolts may experience some stretch due to higher torque applied to meet the tightened spec, best not to reuse those bolts. In really key areas it's not a bad idea to use wired/drilled bolts, particularly if you're taking your car on track. Suspension failure at 50mph is much different than failure at 130mph.

Regular inspection is important too. Once a month or so inspect your suspension - look for corrosion, look for wear, loose bolts, etc.

Lots of fancy talk about exotic materials and engineering. Who cares. Tell me what race teams use and be done with it.

Id be surprised if above grade 8 or 10.9 from reputable sources