This is a KALT T-2 (M42x0.75 pitch) mount (Female) to a C-Mount (Male 1"x32TPI) adapter used for various cameras attached to a Microscope photo tube, or telescope with a T-mount (M42x0.75 metric thread). It can convert T2 mount port or T2 mount microscope trinocular phototube to a C-mount type. You can then mount C-mount threaded cameras on top of this adapter. Picture 1 shows the inside T2 mount thread (M42X0.75). Picture 2 shows the male C-mount thread.