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 come with the rings. You can use them as a basis
for your own mounting blocks as these mount to the rings
$449 includes shipping.
If you are at all interested, please contact me.
My wife would be pleased.