Glock 21 sights & optics

Here you find the Glock 21 accessories and upgrades we have for sighting: optic plates and red dot mounts that put a red dot on your Glock 21, red dots that fit the optic cut directly and iron sights. Everything on this page is made for the Glock 21, so you only need to pick the right group for your slide.

Putting a red dot on your Glock 21

How you mount a red dot depends on your slide. Each version of the Glock 21 takes a different part:

• Glock 21 MOS (gen 4 and gen 5): an optic plate goes into the factory optic cut and takes the red dot. We have plates for the Trijicon RMR, Shield RMSc, Holosun K-series, Leupold DPP, Docter, C-More RTS, Aimpoint Acro and Holosun 509T footprints. See Optics ready plates for Glock 21 MOS [gen 4/5].
• Glock 21 without an optic cut: a red dot mount goes into the rear sight dovetail in place of the rear sight. No milling, no permanent changes, and you can put the rear sight back at any time. We have mounts for the Trijicon RMR, Shield RMSc, Holosun K-series, Leupold DPP, Docter and C-More RTS footprints. See Red dot mounts for Glock 21.

If you have a MOS slide and want to skip the plate, the Holosun SCS MOS, Osight SE MOS and Vector Optics Frenzy 1x16x21 for Glock MOS fit the optic cut directly. See Direct-fit red dots for Glock MOS [G17, G19, G26 & other].

Which Glock 21 do I have?

If your slide has a factory optic cut closed by a cover plate, it is Optics Ready. A slide without a cut is the classic version and takes a mount.

Choosing a plate or mount by footprint

Every plate and mount takes one footprint or a group of footprints. Find the footprint of your red dot in its specifications and take the plate or mount that names it. The type letters (type A, type S…) differ between makers, so always read the footprints in the brackets. They come in steel or aluminium: aluminium is lighter, steel is heavier and robust.

Sights for the Glock 21

Our iron sights for the Glock 21 come from Angry Bear, Eemann Tech, LPA, Night Fision and Zendl. All of them fit the classic and MOS slide. If you use a red dot, choose tall co-witness sights so you see them through the window. Standard-height sights do not co-witness with a red dot. For help choosing between the sight pictures, see Sights for Glock 21.

Frequently asked questions

Which red dot fits a Glock 21?

Any red dot whose footprint matches a plate or mount for your slide. For the Glock 21 MOS we have plates for eight footprints and for the classic slide we have mounts for six footprints. The Holosun SCS MOS, Osight SE MOS and Vector Optics Frenzy for Glock MOS fit the MOS cut without a plate.

Do I need a plate for a red dot on my Glock 21?

On a MOS slide, yes, unless you choose a direct-fit red dot. A classic slide takes a mount instead.

Can I install it at home?

Yes. A plate or a direct-fit red dot needs no gunsmith and no milling: remove the cover plate from the optic cut, put the plate or red dot in and screw it down. A mount needs a sight pusher or a punch to drift the rear sight out. Put a drop of threadlocker on every screw.

Do the iron sights work with a red dot?

Only tall co-witness sights. Standard-height sights are hidden by the red dot.