A "real world" M12 will have either a 17mm or a 19mm head, not a 14mm one. Besides, the strongest M12X1.25 steel bolts will have only a 105 ft-lbs torque rating. To break it free, figure 20% more, sp 126 ft-lbs. And as the fine pitch fasteners are typically used only in engines, corrosion shouldn't be a real world issue. A Grade 8 1/2" with coarse pitch will yield at approximately 155 lb-ft. Figure it would take another 20% after yielding to fail.
You are right about the head size, I had a brain fart. However I think I have come across 12mm with 14mm head (Nissan Patrol drive shafts), but I could be wrong about that and even if not, it has little to do with this discussion. So thanks for the correction!
I disagree with you about the torque required to break bolts free. It can be multiple of max torque for the fastener. This happens for example when bolts have long shank that is corroded and stuck in whatever part the bolt is holding in place. (exhaust manifolds, heavy truck transmission, transfer case housings, brake calipers, ... etc. In order to remove them you have to use all the torque the bolt shank can take. Not the threaded part. This is very clear when you twist the head off, inches away from the threads.
Flange head bolts, turning the flange can require lots of torque all by itself (Crankshaft bolts). Nuts/bolts with deep conical seat (wheels). I have come across many 12mm wheel studs where 1/2" drive tools didn't budge them. Twisted extensions and broken square drives. This spells north of 500 lb ft. Needless to say the threaded part on the 12mm bolt had little to do with all that friction, only capable of ~150 lb.ft max like you pointed out. Not that anyone is suggesting using ratcheting wrench on wheels, I am just trying to explain what can and does effect torque required to break fastener free.
So, even if a wrench survives this test, it's entirely possible it won't survive long in the hands of the average lube guy.
