Which Red Dot Fits My Pistol? A Plain-English Footprint Guide

Last updated: October 26, 2026

Short answer: A red dot fits your pistol when the optic’s footprint, meaning its screw pattern and base shape, matches the cut in your slide or the adapter plate on it. Find your slide’s cut first, using the gun maker’s guide, then pick an optic with that footprint or buy the plate that converts it. Common footprints include Trijicon RMR, Shield RMSc, Holosun K and Aimpoint Acro.

The most common optic question we get is not “which dot is best.” It is “will this one fit my gun?” Fair question. There is no single standard, every maker has its own words for things, and the wrong guess means a box going back in the mail. Here is how to get it right the first time.

What a footprint is

The footprint is the bottom of the optic: where the screw holes are, how far apart, and the shape of any posts or recesses that lock it in place. Your slide, or the plate bolted to it, has a matching pattern. If the two match, the optic screws straight on. If they do not, you need an adapter plate, or a different optic.

Footprints you will hear about most:

• Trijicon RMR. A common full-size footprint. Trijicon says the RMR Type 2 has the same footprint as the original Type 1 (Trijicon).
• Shield RMS/RMSc. A common micro-compact footprint, used on carry guns like the Glock G43X and G48 MOS and the Springfield Hellcat OSP, per Sig Sauer and Glock.
• Holosun K. Holosun’s slim footprint for micro-compacts. The HS507K-X2 is listed as “Direct Mount K Footprint” (Holosun).
• Aimpoint Acro. An enclosed-emitter optic with its own “integrated Acro interface.” It mounts with a plate made for your gun (Aimpoint).
• DeltaPoint Pro. Sig’s ROMEOZero-Pro fits “all DeltaPoint Pro footprints” (Sig Sauer).

Some optics share a footprint with these and some do not. The optic’s product page or manual is the final word.

Step 1: find your slide’s cut

Start with the gun, not the optic. Look up your exact model in the gun maker’s optic guide, or check the box and manual. “Optics ready” by itself does not tell you the footprint.

Glock MOS (full-size and compact)

Per Glock’s optic mounting page, Gen4 and Gen5 MOS pistols now come with a single adapter plate that fits Trijicon, Ameriglo and Holosun optics, except the Holosun 509. Other optics need a different plate.

Standard-frame Gen6 pistols come with three plates:

• 02 plate: Trijicon RMR, RCR, RMR HD and SRO; Holosun 508T, 407C and 507C/Comp; C&H Precision.
• 03 plate: C-More.
• 04 plate: Vortex Defender ST/XL, EOTech EFLX and Leupold DPP.

One wrinkle with the RMR. Trijicon says that to mount an RMR on a Glock MOS, Springfield OSP, Walther PDP or H&K VP9 Optics Ready, you need its RMR mounting kit, part AC32064 (Trijicon). That is on top of the plate.

Glock Slimline (G43X, G48 and friends)

The Slimline MOS pistols are cut for micro optics and do not use plates. Glock says there are two cuts (source):

• Slimline MOS: fits the Shield RMSc footprint and uses M4 screws.
• Slimline MOS-K: fits either the Holosun K or the RMSc footprint, with M3 screws from the optic maker.

To tell which you have, check the item number on the sticker on the handle of your pistol case. The standard cut says “MOS,” and the MOS-K cut has “MOSK” near the end. When Glock launched the G43X and G48 MOS in 2020, it noted the slide cut is not the standard MOS footprint (Glock press release).

Sig Sauer

Sig’s red dot page spells out its own optics. The ROMEOZero and ROMEOZero Elite fit all P365X and XL variants and all Shield RMS/RMSc footprints, including the Springfield Hellcat OSP and Glock G43X/G48X. The ROMEOZero-Pro fits Sig PRO and R2 optic-ready slides and DeltaPoint Pro footprints. The ROMEOZero R fits Trijicon RMR footprints.

Everything else

Springfield, Smith & Wesson, Walther, H&K, CZ and others each have their own systems, and some use plates. Look up your exact model and slide on the maker’s site. Aimpoint, for example, sells separate Acro mount plates for Glock MOS, Sig P320, S&W M&P9, CZ P-10 C, H&K SFP9, Beretta APX and more (Aimpoint Acro).

Step 2: match the optic, or buy the plate

• Direct mount: the optic’s footprint matches your slide cut. Fewest parts, lowest height.
• Plate: a plate converts your slide to the optic’s footprint. Use the one the gun maker or optic maker lists for your exact combo.
• Footprint converter: some optic makers sell plates to swap between their own footprints. Aimpoint lists ACRO/RMR and ACRO/MICRO converter plates, for example.

Step 3: use the right screws

Screws are where a lot of good setups go wrong. Use the screws the gun maker or optic maker specifies for your exact slide and plate. Glock says the cover plate screws on Slimline models are for the cover plate only, and that optics mount with the M3 screws provided by the optic maker. Holosun ships the HS507K-X2 with both M3x12 and M4x12 screws, so pick the pair that matches your slide. If in doubt, ask before you torque anything down.

Want us to mount it?

Our gunsmithing shop mounts pistol optics on optics-ready slides. That is mounting only, with no slide machining, so the slide has to be cut for the optic or a plate already. Shop red dot sights, red dot mounts and plates, or semi-auto handguns.

Frequently asked questions

What is a red dot footprint?

A footprint is the screw pattern and base shape on the bottom of a red dot. Your slide cut, or the plate on it, must match it for a direct fit. Common pistol footprints include Trijicon RMR, Shield RMSc, Holosun K and Aimpoint Acro. Check the optic maker’s fitment notes, like Holosun’s, to confirm.

How do I know which red dot fits my pistol?

Start with the gun. Look up your exact model in the gun maker’s optic guide, then pick an optic with that footprint or buy the matching plate. Glock’s optic mounting page, for example, lists which optics fit each of its plates and Slimline cuts.

What red dot fits the Glock 43X or 48 MOS?

Glock says the standard Slimline MOS cut fits the Shield RMSc footprint with M4 screws, and the MOS-K cut fits Holosun K or RMSc footprints with M3 screws from the optic maker. Check for “MOS” or “MOSK” in the item number on your case sticker (Glock).

Does a Trijicon RMR fit a Glock MOS?

Yes, with the right parts. Glock’s Gen4/Gen5 MOS plate fits Trijicon optics, and the Gen6 02 plate lists the RMR. Trijicon says an RMR on a Glock MOS also needs its RMR mounting kit, part AC32064 (Trijicon). We carry the Trijicon RMR mounting kit for Glock MOS and the RMR Type 2.

What red dot fits a Sig P365X or P365XL?

Sig says the ROMEOZero and ROMEOZero Elite fit all P365X and XL variants and all Shield RMS/RMSc footprints, including the Springfield Hellcat OSP and Glock G43X/G48X (Sig Sauer). For any other optic, check that maker’s fit list for your exact P365 slide.

What is the Holosun K footprint?

It is Holosun’s slim footprint for micro-compact pistols. The HS507K-X2 is listed as “Direct Mount K Footprint” and ships with M3x12 and M4x12 screws (Holosun). Glock’s Slimline MOS-K cut accepts K footprint optics without a plate (Glock). We carry the HS507K-X2 with the ACSS Vulcan reticle.

Do I need an adapter plate for my red dot?

Only if your slide cut does not match the optic’s footprint. Many optics-ready pistols ship with plates, like Glock’s Gen6 02, 03 and 04 plates (Glock). Aimpoint sells gun-specific Acro plates (Aimpoint). Use the plate listed for your exact gun and optic.

Still not sure?

Tell us your pistol model and the optic you are looking at, and we will help you sort out the fit. Contact us, or browse red dots and mounts and plates.

Sources

• Glock, Optic Mounting
• Glock press release, optic-ready Slimline G43X and G48 (August 24, 2020)
• Sig Sauer, Red Dot Revolution
• Holosun HS507K-X2
• Aimpoint Acro
• Trijicon RMR Type 2 (RM06-C-700672)

Change log

• October 26, 2026: First published.