I purchased the rings to make a cheap dovetail mount for an old Tasco telescope. The 66mm rings were almost the perfect size.
I screwed the rings on a vixen style dovetail bar to attach the telescope on a motorized mount.
I added additional self adhesive cork strips to the inside of the rings to better grip the tube and prevent any marring of the telescope..
Considering the very low price they work quite well for this application.