Delete comment from: Ken Shirriff's blog
It appears to be an annular ring.
See:
http://www.semiconductormuseum.com/Transistors/Motorola/Haenichen/Haenichen_Page7.htm
and the next page too.
Feb 25, 2019, 11:37:43 AM
Posted to Op amp on the Moon: Reverse-engineering a hybrid op amp module