Need a small hexegonal pocket for allen wrench?

[Rich05]

Push the head into the hole.

very cool idea.

sorry that was a typo .. i meant 5/16.

[peter@slater]

You could also get a 1/8" hex rotary broach, #306-127($49). This will give you sharp corners. Usually you need a broach holder, but it sounds like you could just push it in for a few pieces. 'DareBee' was right, "don't forget to start with your hole, like 1/4" deeper than finished depth required." You will need some room in the bottom of the hole for the chip to curl into. They're in stock with most rotary broach suppliers.

[HIRAH]

i've broached 1/4" hex into steel a bit.
spot drill for a pretty chamfer, drill just under the flats of the id hex,
undercut with a key cutter so you dont have that ugly mess at the bottom, endmill to size, and broach with a hex.
we use ground hexes. we also drill a thru hole to help the air escape.

[SQT18MS]

There are tool to do this with you know

But the allen key works just fine, you could even drill the hole a little larger than the allen key are on the flats.

I have the tool to do this on large series, its like a coned allankey in HSS and its out of senter but its angled too so that the allan like HSS tap hits the senter anyway. I usaly rut the tool at 250 to 400 rpm i mild steel. (ST52-3)

If its just one or two parts I would go for the allan key tric

[MFassler]

you could do it the old school way and watts drill it,or edm it or broach it the list goes on.