This mounting standard of the thread type was first used by Guide. Gradually, more night vision and thermal clip-on manufacturers started using it; today, it is one of the most frequently used clip-on mounting standards along with M52x0.75 (Dedal mounting standard). Most mounting solutions for it are two-piece, a combination of an adapter designed for the M52x0.75 thread and a suitable reduction ring (converter). All the clip-ons that feature this mounting standard are front-mounted, meaning that they are mounted on the riflescope’s objective.
Guide mounting standard (M33.5x0.75) on Steiner Nighthunter C35
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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 Guide mounting standard (M33.5x0.75) 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