I had a square block for holding 5c collets. When I first tried to use it I found that I had not tighted the nut enough at the back of the collet (hand tightened) and the part ended up moving in the mill. I didn't have a spanner/pin wrench but did have some aluminum rounds, so I made a wrench. Also redrilled the holes in the nut since they were out of line all the way around. Simple project but works well. Pictures below.
