Crown Bolt Head Markings

[Drassk]

OK, I've been digging through my 'bin of bent stuff' lately and, since my workouts are very low volume and I've been away for awhile, I can pick out which bolts I bent when. The point of all this is that I've noticed that I have three different types of crown bolts and have bent quite a few of two of the markings (enough to be certain there is a distinct difference in difficulty). So, without further adieu :

All bolts have the 307A designation, which I think means 'grade 2'. The other letters and difficulties were as follows:

CYI: Universally easy, some bolts prone to being 'duds' even (all are easy but the odd one is -much- easier). I've bent probably 16 of these ones.

OF: Only bent two, but they seem to be significantly harder than the CYIs.

SBY: These are the only ones worth considering once you're serious. CYIs are OK for a warmup but the SBYs start to get challenging. They're universally harder than any of the CYIs and, of then ten I've bent, one was actually much harder than the other ones rather than any being unnaturally easy.

For order from easiest to hardest CYI->OF->SBY

Anyone else bent a bunch of bolts from other companies who's noticed such differences depending on markings (which designate place of fabrication, I'd guess)