This is a precision bit driver adapter I made in Tinkercad. I wanted an adapter to use my precision bits in my power screwdriver that would allow me to use both my 4mm bit set and my 3.5mm bits from my reversible screwdriver. I tapered the inside hole so it would fit the shorter 4mm bits and my longer 3.5mm bits. I chamfered the back end and added a hollow along the neck so it would work with driver extensions with ball bearing retainers.

I printed this on my Printrbot Simple Metal with 20% infill and it is very sturdy.