2″ locking ring (for Celestron SC’s 8″/9.25″/11″/14″), with thread
female 2″ (5mm optical length).
The counter ring allows the direct connection of star diagonals
the SC thread connection, without using a 2″ sleeve. That saves
about 50mm length. Whenever there is little space at the back of the device
and you still want to use 2″ accessories. A good example
are fork-mounted Schmidt-Cassegrains. With normal adaptation of
Diagonal mirror with SC thread or 2″ plug could not be used with the device
pivot more.