This piece came to our club with a 14" Meade LX200 SCT. It doesn't fit anything we have...It may have been associated with a 14" Ritchey -Cretien used as an upgrade from the Meade for astrophotography.
The straight tube measures 2.010" i.d. and 2.500" o.d with two clamping screws. The mirror itself is adjustable with 3 tiny setscrews.
The other end has a swivelling female thread piece, about 50mm in diameter.
What is it?