Allens are hardened, because the head requires that to work at all. This is the primary
benefit, IMO as an ME, for using black oxide allen-headed small screws. Typical yield is
in the 110,000 psi area. Real Grade 8 is 125,000 psi, and only applies to hex head bolts
and the head markings is 8 tic marks. 3 tic marks are Grade 5, pretty decent bolts. No
tic marks are Grade 2......OK for some applications.
Most slotted head small screws are very soft steel. SOME of the SS ones are harder, but there are
some ridiculously soft SS alloys out there. So, of the "ordinary supplier" screws, you are
most likely to get a fairly strong screw (in the # sizes) with an allen head, not because they
are helping you out, but because without a hard head it wouldn't tighten once - the
wrenching hole would round out 1st try, the tougher body is just a side effect -- a very good side effect.
I don't mind paying 10 times a fair price sometimes for two screws that I need NOW. But, if
I need a bunch and not in a big hurry, I'll order a box from one of the online suppliers like
McMaster-Carr. Good stuff, reasonable if you buy 100 screws or nuts, usually. Frequently
pay 2-5% of the onesy price from a hardware store.
Let us know if the Harbor Frt screws are any good......I start out pretty skeptical, but I am
entirely willing to learn. Some of their stuff is abominable, some is pretty decent.
Bill