Drill Side Grip Handle

Wanted a side grip for my drill, but could not find one for sale locally. The side holes on the Hitachi are M10 and approx 1cm deep (although probably this design works for 3/8" holes as well). The bolt I found at the store was M10-1.50-75. This grip feels like a comfortable diameter for my large hands, but is just shy of being long enough for my pinky finger to engage. Overall feels comfortable enough that I will probably not revise.

I should have designed it with a hex-profile on the end, but in the end I just glued the hex corners with superglue and it holds well.