All of the ones that I've seen have been the same thread. There might be some obscure BB's around somewhere.
Those bolts require a good amount of torque, typically 30 to 35 ft/lbs. Imagine a 30 pound weight hanging on the end of a foot long wrench. I always use a torque wrench because, it's a bike part that left to my own instinct, I would undertorque. I suspect that lots of other guys do too. If you scan this forum for a while you will read many posts about crank arms coming loose and being ruined due to undertorqued bolts.