Skywatcher tube rings are built from cast aluminium to create a sturdy support for many mounts / mounting plates from AZ3 , EQ1 up to EQ6. Each is felt lined to help reduce the risk of scratches to the OTA.
Each comes with a piggy back thread mount for cameras. Rings can be slackened to allow rotation. Note that the size in mm shown is not showing what telescope they are for, but is the measurement of the inner width of the rings. For example the 90mm tube rings #20410 (pictured) are suitable for the Skywatcher StarTravel 80mm short tube refractor. If in doubt , ask your local dealer