This adapter threads into the rear of the right ascension axis of the mounts specified below to allow use of the Polar Alignment Scope (these models - PASILL, PASILL2, PASILL3, PASILL4 or PASILL4L). Some 400 mount models require this part to attach encoders as well as the polar scope. This is one of the most common items to be misplaced and we maintain an extra stock if you have lost yours.
Most 1200 mount models (except the original black 1200DA models), all 900 mount models (HDA, QMD, SMD and GTO).
It is also used in some 400 mount models that have been produced.