Forgot to mention , those white strip's around the tube between the rings are Nylon strips about 8mm thick screwed around the OTA and with the rings set with bolts and lock nuts I can rotate the whole OTA with ease without the worry of the HUGE assembly sliding down and getting really , really out of balance very quickly ,
bad at 2am in the dark !!.
.
Balance is achieved via the dovetail but being a massive OTA it takes only an eyepiece like a TV 31 telemangler to upset the balance .
For your information
.
Brian.