The Baader Astro T-2 System - To adapt to guiding Cameras from eyepieces.

This clamp has an optical tube length of 12 mm.  It includes 3 screw clamps.  T-2 clamp number 8C.

The inner diameter / clear aperture is 31.75 mm (1.25-Inch) and the outer diameter is 52 mm (2.05-inches).

The inner connection (lens side) is a T-2 thread (M42 x 0.75) and the inner connection for the eyepiece/ camera side is the clamp at 1.25-inch.