Found it the hard way ... it is a 10 mm x 1.5 pitch.
Can't find a 10mm drill bit in Charleston. Do have a 25/64" which is supposed to cut a 0.3906 hole. (Turns out the 25/64" bit is the tap bit for a 7/16"-20 SAE thread used for the flange bolts.) 10mm translates to 0.3936" ... which would mean I should find a 10 mm bit.
Anyone know the actual diameter of a 10mm bolt? If they run a few thousandths small I can use what I have and have a good tight fit.
Thank you ... I had found this one. Interesting because it is ideal. Got a couple of cheap 8.8s at the local hardware store and they measured 0.384" in diameter. Guess I'll have to wait until the 12.8 bolts come in to see what they actually measure. Hate to do that because I have three days that could go into machine work that will be lost waiting for the darn things!