The 5 and 6 inch Unitron/Polarex refractors have a very unusual double RA axis. There is an outer casing whose rotation is controlled by the worm mounted on the body of the axis carrier and then there is a second worm that controls the motion of a floating axis within the outer casing. This allows the scope to be slewed in RA by disengaging the secondary worm through a lever clutch. When engaged the secondary worm locks the inner axis to the outer casing. A very neat feature!