27/64 mini post rings, with the following part #s:
Bally: R-414, 17-41-633, and 0017-00041-0633
Gottlieb: A-15704 and A-15705
These mini post rings won´┐Żt split when you install them, they have a 1/8” hole in the middle, which is larger than most. A snug fit on the metal post.