A number of companies sell cheap stainless steel hand coffee grinders with a pentagonal shaft where the handle connects; $9 at Walmart last I checked. This is an adapter to drive those grinders with a cordless ratchet or drill; it's intended to sit in a 15mm socket. Printed in PLA with 6 perimeters; print the adapter with the hole pointing up. I'm using this with a 1/2" ancient blue Ryobi cordless drill at 350RPM, so this thing can handle plenty of torque. The inner hole is pretty tight, that was a deliberate decision to spread the load better.