In MEW 59 (Scribe-a-Line) Ted Wale provided a sketch of a chuck back (or mounting) plate and how to size a threaded bush. Subsequent issues (67, 69, 70) discussed the pinning options (two at 90 or 180 deg, 3 at 120 deg), but I have not been able to locate an answer to the original question about the size of the bush relative to the "boss (spigot)" in which the bush was to be secured. The spigot was 2 inches and Ted's colleagues suggested the bush be 1.5 inches, thus equalizing the wall thickness of bush and boss.
Anyone know the answer?
Paul