Originally Posted by
JohnDThompson
Nice. It still could be Swiss thread, as Phil offers Swiss thread mounting rings.
True that, and Phil Wood Swiss rings were only offered in Steel, no alloy versions, plus since they are LH thread on the fixed side that should be one clue, Phil also painted the inner flange with red paint on the fixed ring (same as they did for BSC rings).
So, if you found a LH thread fixed ring with red paint in steel it can be either Swiss or BSC, but on a '72 Moto it could only be Swiss. (RH thread fixed obviously: FR)