This is a very high quality
rotation ring set for a newtonian.
This is a Parks Optical:
"Rotating Ring System 15 7/8" 601-41020"
scopecity shows them for $649
This is for the Parks 16 5/16" OD tube
which has a 15 7/8" ID.
These are in good shape but are 10 years old.
The Nylon bearings were replaced and are quite new.
The paint is poor but the rings are in excellent shape.
Two mounting blocks which were originally used on a Byers
812 mount some with the rings. You can use them as a basis
for your mounting blocks.
$100 includes shipping.
Send me an email and I'll send you a url to more images.