The 20mm thick top plate can rotate inside the column with
the NJP and scope on top. This allows for rough polar alignmnet
with everything in place and without having to physically move the pier.
Once rough polar alignment is achieved the plate is locked in place by
the three set screws. These set screws insert into a grove milled into
the top plate so that the upper assembly cannot topple off by accident
even while the set screws are loosened during rotation.

Please contact me if you would like a pier like this one m.sidonio@bigpond.com