Rivnuts or nutserts for windows / headlight covers etc...

Andrew

Supporter
I'm looking to call on the vast experience of the forum to guide whether it's best to use rivnuts or nutserts to secure my side / rear windows, head & fog lights covers - I'm leaning towards using M3 fittings due to space constraints installing both options..... down the a-pillars of the doors being the size pinch point.

I understand the rivnuts could crack / deform the fibreglass when crimping, nutserts may not have sufficient 'bite' to hold then securely in places where I can't reinforce the back with a 2 part epoxy adhesive.

I don't want to just screw into the fibreglass (how my covers and windows had been previously fitted....

Thanks as always!
 
Hi Andrew,
I used M3 aluminum riv-nuts, but super-glued them in. As the screws aren't going to be that tight, this is fine and if it does come loose, it's easy to remove as the body of the riv-nut has not been distorted
Regards,
Andy
 

Neil

Supporter
Andrew, lets first define what is a "Rivnut" and what is a "Nutsert", these terms are usually mis-applied.

Rivnut: These were originally developed by Goodyear for attaching rubber de-icing boots to the leading edge of aircraft wings and called a "Rivet-Nut" because they function like a "Pop" rivet. They expand from the rear so they are very suitable for use in thin metal or where the material is softer, such as fiberglass. Adding a washer behind the Rivnut adds to its pull-out strength and adding a bit of epoxy to the hole before placing the Rivnut increases its torque-out strength- the main problem with these types of inserts.

Nutsert: This type of threaded insert breaks into to two concentric parts as it is tightened, wedging one inside the other and expanding its diameter to fit tightly into a hole. It will NOT work in thin sheet metal or soft materials. The hole size is more critical as is the hole surface finish, perpendicularity, etc. These will work on a completely blind hole where a Rivnut will not. Epoxy helps a Nutsert, too.
 

Andrew

Supporter
I'd thought about a nutsert suitable for wood backed with epoxy but like I mentioned, I'm considering ALL options :)

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Bill Kearley

Supporter
The nutsert with epoxy, make sure the hole isn't to small when installing. A good thin foam tape weather strip on the window and you're good to go.
 

Terry Oxandale

Skinny Man
If you're still working with an unfinished panel, the for-wood nutserts installed with resin/glass in a snug-sized hole works well. I've used this for the rear spoiler on a fiberglass panel, and have never had an issue. For finished panels where you don't want to mar any of the existing work, a superglued Helicoil is the best option. Clean, and holds very well. I've done this for the windows. As always, you want the affixed part to make contact with the insert itself, and not the panel material around it, else you create divots or dimples over time when torqued down.
 

Andrew

Supporter
Thanks all for the input, it seems helicoils are the preferred choice...... and these would still work in fibreglass panels where they are maybe only 1mm think? I can't imagine I'd get a decent tap prior to winding in the coils
 

Chris Kouba

Supporter
Not sure there's a formula for it but I know I'd feel a lot better if there was full coil depth thickness if possible. More would be better...
 
Just curious, can't you just use regular screws directly into the fibreglass?
Seen it on a lot of GT40's (FIA cars) at the racetracks.
 

Terry Oxandale

Skinny Man
Just curious, can't you just use regular screws directly into the fibreglass?
Seen it on a lot of GT40's (FIA cars) at the racetracks.
I used to actually tap the fiberglass, and 90% of the time that worked well...until a little too much torque was applied, and it didn't have to be much (was pretty reliable if I had at least a 3:1 ratio of length to width of the thread size--e.g. 20mm threaded bore for a 6mm x 25mm fastener). I've also used coarser screws to do the same, with the same results. Once that the threads are stripped (which won't happen with the inserts properly affixed) in the fiberglass panel, you've got a mess. It's just so much more secure, sanitary, and professional to use the inserts rather than depend on the glasswork staying good.
 
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