This thing enables the use of 4mm bits in screwdrivers made for the larger(standard) interchangeable screwdriver handles. The V2 design is open on both ends which allows the bit to be held in place via the magnet in many screwdrivers. My tests show there are a wide variety of tolerances in the standard driver handles meaning the adapter could not be easily made to friction fit and could slip out in some cases.

V3 added a thin layer to the the bottom of the adapter. It's thin enough that magnetic screwdriver will hold the bit and the adapter in. This is a superior arrangement in most cases.

PLA is strong enough for this design and has worked quite well for me. No supports, rafts, or brims are needed. Pretty much any infill should be fine.