Glock MOS Optic Fitting Guide: Which Plate for Which Red Dot

Glock's MOS (Modular Optic System) slides are milled for optics but almost never fit one directly — you need the right adapter plate for your optic's footprint. Get the plate wrong and the optic either won't bolt down or will shoot loose. Here's the match-up.

Step 1 — identify your optic's footprint

The footprint is the pattern of screw holes and recoil bosses on the optic's base. The common ones: RMR (Trijicon RMR, Holosun 407C/507C/508T), K footprint (Holosun 407K/507K, EPS, EPS Carry — closely related to RMSc), and Holosun 509T (its own lug pattern). Full reference: our footprint compatibility chart and RMR vs RMSc explained.

Step 2 — match the plate

Genuine Holosun plates beat generic ones for a simple reason: correct recoil-boss engagement machined for the exact optic, with the right screws in the bag. Browse all mounting plates and Holosun mounts & plates.

Step 3 — fit it properly

• Degrease everything — screws, plate, slide threads — before assembly.
• Blue (medium) threadlocker on plate-to-slide and optic-to-plate screws. Never red.
• Torque: follow the optic maker's spec (typically around 15 in-lb for optic screws — check your manual; snug + threadlocker beats gorilla-tight).
• Screw length check: optic screws that are too long bottom out in the slide and leave the optic loose while feeling tight. If the optic rocks after torquing, stop and check.
• Witness-mark the screws with a paint pen, then re-check after the first 100 rounds.

Step 4 — zero it

Full walkthrough in how to mount and zero a red dot. For carry guns, confirm zero at 10 and 25 metres.

Not sure which optic to start with? See best pistol red dots and best optics for concealed carry, or browse all pistol dot sights. UK-stocked, fast tracked dispatch.