...the round bit on the following?
I could file it and probably get reasonable accuracy, but I was wondering if there's a way to machine it. I have a mill and a lathe. No fancy milling cutters. Material is aluminium. The best I can come up with is to turn a 4mm pin and hold that in a vice on the mill, while I take light cuts by rotating the thingy around the pin with it held in vice grips or similar. Is there a better way?