This is a screwdriver handle which can be used with bit holders. You can buy bit holders from most hardware stores or Amazon, I used these ones - https://www.amazon.co.uk/dp/B01875O528/ref=pe_3187911_189395841_TE_3p_dp_1

I designed it to be ergonomic and made it more ball like so when pushing the screwdriver into screws it is comfy in the hand.

You may have to scale the handle up/down depending on your printer tolerances but I printed it so that the handle had to be hammered onto the bit holder. If the bit holder is too loose in the handle it will round out the hole very quickly.