The right hand end is 1.25" that goes into your scope, the vertical part takes your reticle and the left hand side is a sliding tube that you attach your webcam to. There is a standard T thread at one end (hence the need for a T adapter for the webcam, but I "believe" that you can remove the tube and there is a standard 1.25" hole with securing screw inside the tube, but can't swear to it.
I should have said before that didn't have the third screw, as I don't have it anymore. The mirror didn't agree with the concrete when they met with significant speed
Steve has his phone number at the top right hand side of the page under the "contact" link. 02-9905 0757