This rubber is measured by it's OD (outer diameter).
All other ring measurements other than this mini post are ID (inner diameter) measurements.
This mini post is slightly smaller than the 7/16" OD mini post.
Williams/Bally reference numbers 23-6626 & 2A-4003.
Stern #545-5348-19 & 545-5348-69.
Bally #R-206-11.
Gottlieb #A-14793.
Classic Stern #7A-125.
American Pinball #RBR0003-00.
Jersey Jack Pinball #25-006005-06 & 25-006003-06-0.
25-006003-06-0