This mounting standard is named after Holosun 509T, a compact, enclosed reflex red dot sight that was the first to feature it. It is made of two grooves and a recoil stop close to the center of the mounting surface. The design of the mounting surface is similar to the Aimpoint Acro mounting standard and the Picatinny mounting standard. One of the grooves can be moved with a screw. There are no screw holes on the surface itself – fixing the adapter in place is done with the screw on the side.
Holosun 509T footprint
Red dot sights with the Holosun 509 mounting standard can be used on handguns and rifles.
Most adapters designed for this mounting standard are made from aluminium. They are mainly produced by Holosun.
Holosun 509T mounting standard
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