Remix of atvking's hex inserts for the Prusacaster.

Tweaked to print in PLA-Silk, and split into three plates.

These are also placed front side down to allow etched smooth (hot plate) texture transfer.

Added a 4 mm brim for bed adhesion and thermal stability while printing.

Recommend using a very small amount of fast-set epoxy to assemble these. Even with a slight friction fit, they can come loose unless more time is spent tweaking tolerances / sclaed dimensions.