I use O-1, also called 1095 tool steel (oil hardening, .95 carbon) . I've not been able to find in hex or octagon stock these days and I buy round drill rod.
The last batch of so-called 0-1 I got from MSC turned out to be air hardening steel and we couldn't anneal it after forging. It turned out to be a complete waste. I haven't found another reliable source but I'm sure oil hardening steel is available.
I've made tools from Allen wrenches but always wonder what kind of steel it is. I just grind without annealing, hardening or re-tempering.
