Note: groups.io will be down for maintenance on Wednesday, October 5th, starting at 9AM Pacific Time (4PM Wednesday October 5, 2022 UTC), for approximately one hour.
Hi again George
It might be worth checking with Astro-Physics to see if they still have any of the machined safety stop knobs that fit the old counterweight shafts that used the 5/16-18 thread for the stop. The catalog number was MSSKB.
I bought one of these in late 2016 to use on my old 800 mount. The cost was $27.00. As with all things Astro-Physics, the quality is excellent, and the machined aluminum is much more durable than the phenolic knobs.