This thread-type mounting standard is quite rare – it is used predominantly on Armasight clip-on devices. There are no single-piece mounting solutions on the market – a reduction ring (converter) must be paired with an adapter that goes on a riflescope’s objective. All the clip-ons that feature this mounting standard are front-mounted, meaning that they are mounted on the riflescope’s objective.
With Smartclip, Rusan, Recknagel, and Präzise Jagen adapters you need to choose the size based on the outer objective diameter of the riflescope.
Our list of riflescopes and their outer objective diameters is available here
Rusan reducing ring for the Armasight mounting standard (M39x1.0) can be paired with Rusan, Smartclip and Recknagel adapter for the M52x0.75 mounting standard.
Our article with all the mounting standards on NV and thermal clip-on devices is available here