I think the bolts are M8x50mm. I bought 4 Stainless Steel from an industrial fastner supply house. I also replaced the brake & clutch resevoir cap bolts (M4x10mm) with stainless bolts. Instead of using a phillips screwdriver, I now use an allen wrench.
But I always try to replace with stainless whenever I can (non structural and change it from a phillips head to an allen head bolt). A little polishing on a buffer wheel and they shine up real nice and never ya have to worry about rust!!
Thanks for the measurements Snore....I stopped by a fastner place up from the house and got 4 hex head for the seat. The guy didn't have any stainless, only black. He didn't charge me for them, he kinda felt bad because he knew they were going on my seat and I wanted stainless or chrome. I guess Harley riders aren't all bad!:cooldevil:
I will be getting some allen head to replace the ones on the brake and clutch lids!