In article , Pete Snell
wrote:

Hi All;

I need to make a special 'box end' wrench for a particular job I do
frequently. It's not complicated, overall dimensions would be about
1.25" X 6" X 1/4". One end would have the special shape machined in, and
the other end would have a 3/8" square hole for a 3/8" ratchet. Regular
mild steel deforms with regular use, so I lose the good fit on the
fastener after I've used it a couple of times. I want to use some
tougher stuff, but I'm not sure what would be best. 4130 hardened and
tempered after machining?

Pete

O-1 flat ground fully annealed tool steel is available from any decent
industrial supplier.
It is a very easy steel to deal with and quite good for wrenches.
There are better steels, but they are harder to find and harder to heat
treat.
Another good steel would be 4340.