What is this part?

[bendiddley]

This came with some stuff I bought the other day. Not sure what it is or what its used for. The male thread is 53mm, the female thread is 42mm.  I assume it's a T2 adapter of some kind, but not sure exactly. Also not sure what the holes in the top are for, is it for tightening? Hope someone can shed some light. Cheers.

[tooth_dr]

That fits to a filter wheel, to step the opening down to M42, allowing a camera to attach directly to the FW with as low a profile as possible.  It sits quite flush so those holes are for loosening or tightening.  (Thats my educated guess )

Edited October 8, 2019 by tooth_dr

[bendiddley]

On 08/10/2019 at 17:16, tooth_dr said:

That fits to a filter wheel, to step the opening down to M42, allowing a camera to attach directly to the FW with as low a profile as possible. It sits quite flush so those holes are for loosening or tightening. (Thats my educated guess )

Many thanks!

[midatlantic61]

The two holes are used to un/tighten the adapter with the following tool:
https://www.rothervalleyoptics.co.uk/rvo-eyepiece-maintenance-tool.html