Tele Vue T-Ring Adapter for 4x Powermate

Yes, the Tele Vue T-Ring Adapter for 4x Powermate has a M42x0.75 threading.

It has T-threads. T_threads are approximately 42mm

First, note that this adapter is of no use unless you have the newer version of the 4x Powermate that separates in the middle. This adapter replaces the half of the Powermate that normally holds the eyepiece and allows the Powermate optics to be more rigidly mounted to the camera. The male threads of this adapter mate with female threads of the T-ring mounted in place of the lens on your camera. If you are using a camera that you know lacks a UV-IR cut filter, a 48mm UV-IR cut filter can be screwed into the bottom end of the Powermate where light enters from your telescope. Note that off the shelf DSLRs generally have built-in UV-IR cut filters so that colors come out close to the intensity seen by the human eye and therefore generally don't need another UV-IR cut-filter. Astronomical CCD cameras, and DSLRs that have had their UV-IR cut filter removed, and security cameras (with extended IR sensitivity) may give sharper images with a UV-IR cut filter, especially when using a refractor (lens based) telescope, since refractor optics often aren't corrected well for UV and IR light.