Instructions
I print these on a 1-layer raft, then just clear the holes with a 5mm and then 8mm drill held in the hand.
Fit a washer onto the M8 axle, and put the race on top. Load one BB into each hole and sandwich with another washer.
Thick grease or vaseline stops premature discharge of the BBs. They can be printed in most plastics including PLA, ABS and CAPA.