Glock MOS & Optic Footprints

RMR, Holosun K, RMSc, DeltaPoint Pro, ACRO, 509T, A-CUT, Gen4/Gen5 MOS, Slimline MOS, MOS-K and Gen6 — what actually fits what, when you need a plate, and why two optics that look almost identical underneath still may not mount the same.

Glock   |   Optics & Mounting   |   Forge Files

Red-dot compatibility should be easy.

Figure out the footprint. Buy the optic. Bolt the damn thing on.

Except now we have RMR, K, RMSc, DPP, ACRO, 509T, A-CUT, old Glock MOS plates, Slimline MOS, MOS-K, Gen6 plates, direct-milled slides and adapter plates stacked on top of other adapter plates.

And manufacturers love using phrases like “RMR compatible” when what they sometimes mean is:

“We included an adapter that eventually gets you there.”

That's not the same thing as the optic having an RMR footprint.

So this guide is about the actual mechanical interface — not whatever marketing label got slapped on the box.

“Fits an RMR plate and has an RMR footprint are not always the same damn thing.”

Gen4 / Gen5 standard MOS: uses an adapter plate between the slide and most optics.

Standard Slimline MOS: factory cut is based around the Shield RMSc footprint.

Slimline MOS-K: revised cut accepts both Holosun K and RMSc-family optics directly when the optic and hardware are compatible.

Gen6: completely different Optic Ready System using three factory plates numbered 02, 03 and 04 for Glock's supported optics.

A-CUT is not ACRO. Glock's A-CUT is the Aimpoint COA wedge-style interface. Aimpoint ACRO uses its own completely different ACRO interface.

Holosun K is not exactly RMSc. They're closely related, which is why adapters and modified cuts exist, but don't blindly treat them as identical.

Holosun 509T has its own footprint. Holosun supplies an RMR-to-509T adapter with current 509T models.

Know the slide cut before buying the dot. That's easier than buying a $400 optic and then finding out you need another $80 plate to make the damn thing fit.

The footprint is the mechanical interface between the bottom of the optic and whatever it's mounting to.

That includes more than two screw holes.

A footprint can involve:

• Screw-hole spacing
• Screw diameter and thread
• Front recoil bosses
• Rear recoil bosses
• Boss diameter
• Boss height
• Length of the mounting surface
• Width of the mounting surface
• Special rails, wedges or clamping surfaces

That is why two optics can use screws in nearly the same locations and still not be true direct-fit replacements.

The bottom geometry matters.

This is the Glock MOS system most people are talking about when they say “Glock MOS.”

Certain Gen4 and Gen5 standard-frame pistols use a large rectangular slide cut.

An adapter plate goes between the Glock slide and the optic.

So you effectively have:

Current Glock standard MOS pistols sold in the U.S. come with a single included plate Glock says supports Trijicon, Ameriglo and Holosun optics except the Holosun 509 family.

Other footprints require the appropriate Glock or aftermarket plate.

The important thing is that old-school MOS is a plate system. It is not one giant universal optic footprint.

The G43X MOS and G48 MOS do not use the same big adapter-plate cut as a G17 MOS or G19 MOS.

They're narrower guns, so Glock built a narrower direct-mount system.

Glock currently identifies the standard Slimline MOS cut as fitting the Shield RMSc footprint.

The standard cut uses M4 optic screws.

This is where people get into trouble with Holosun K optics.

The K footprint and RMSc footprint are close relatives.

They're not automatically identical.

Depending on the optic and exact slide cut, a K-footprint optic on a standard Slimline MOS may require an adapter interface instead of simply dropping straight onto the slide.

Glock eventually cleaned up the K-footprint problem with the MOS-K cut.

Current Glock guidance says MOS-K accepts:

• Holosun K footprint
• RMSc footprint

without requiring a traditional adapter plate.

MOS-K also changes the optic hardware to M3 screws.

And remember: the little screws holding the factory cover plate on are not your optic screws.

Glock even labels MOS-K separately on the pistol's case sticker, so check what you actually own instead of assuming every G43X MOS cut is identical.

Gen6 threw the old standard MOS setup in the trash and started over.

The G17 Gen6, G19 Gen6 and G45 Gen6 launched with Glock's new Optic Ready System.

Standard-frame Gen6 pistols ship with three plates.

Instead of the old architecture where the optic mounts to a plate that is separately fastened to the slide, the Gen6 system uses the plate to establish the correct mounting interface while Glock's specified hardware secures supported optics through the system into the slide.

So don't buy a Gen5 MOS plate for a Gen6 and expect it to work.

This chart is useful because it tells you what Glock itself currently supports.

It does not mean every optic that looks like one of these automatically belongs on the same plate. Check the exact optic.

The Trijicon RMR interface became one of the closest things the pistol-optic world has to a full-size industry standard.

That is why you'll see a huge number of slides and plates marketed around the RMR pattern.

Common optics in the practical RMR-style ecosystem include:

• Trijicon RMR
• Trijicon RMR HD
• Trijicon SRO
• Trijicon RCR
• Holosun 407C
• Holosun 507C
• Holosun 507Comp
• Holosun 508T

Glock currently groups those optics together on Gen6 Plate 02.

That's good practical evidence that if you're building a full-size Glock optic ecosystem, this family gives you a ton of choices.

Still check the specific slide and hardware instead of assuming every “RMR style” optic is dimensionally identical in every possible detail.

The K footprint is the big one to understand for slim carry guns.

Holosun currently identifies optics such as the following as direct K-footprint optics:

• 407K
• 507K
• EPS Carry
• EPS full-size

That last one surprises people.

The full-size EPS has a wider body, but Holosun still lists its direct mounting interface as K footprint.

Current EPS models are even sold with adapters that expand compatibility to other mounting systems.

This is why you have to separate optic body size from footprint.

RMSc is another major micro-pistol footprint family.

The original Glock G43X MOS / G48 MOS factory cut is explicitly built around RMSc-style mounting.

The reason RMSc and K get confused is because they're closely related and aimed at the same basic slim-pistol market.

But the recoil-lug / boss arrangement can differ.

That's why:

• Adapters exist
• Some slides are specifically modified for K
• Glock created MOS-K

If they were always identical, none of that would be necessary.

Simple version: RMSc and Holosun K are close enough to create constant confusion, but different enough that we still verify the exact cut. Glock's MOS-K specifically supports both, which is a much cleaner answer than pretending they're identical.

The 509T is where people get fooled by the adapter.

Current Holosun 509T models use a:

509T footprint.

They are supplied with an:

RMR-to-509T adapter plate.

That means the optic can be adapted onto an RMR-compatible mounting surface.

It does not mean the 509T itself has an RMR footprint.

Even Glock's current standard MOS page specifically excludes the 509 from the optics supported by its included standard plate.

This is the perfect example of why “compatible with RMR” and “RMR footprint” need to stay separate in your head.

ACRO doesn't use the normal two-screw-through-the-top layout people associate with RMR/K-style dots.

Aimpoint identifies the P-2 as using its integrated:

ACRO interface.

The optic clamps onto the appropriate ACRO mounting interface.

Aimpoint sells a dedicated plate for Glock MOS, along with ACRO plates for other optic-ready pistols.

So if your Glock slide is milled for RMR:

an ACRO P-2 does not magically screw directly into that cut.

You need the correct interface.

Same optic company.

Completely different mounting system.

Glock's A-CUT system was developed around the Aimpoint COA.

Instead of mounting with the traditional optic screws through the top, Glock describes A-CUT as using a patented wedge-style connection that locks the optic directly to the pistol.

So:

ACRO and A-CUT are not interchangeable names.

The Leupold DeltaPoint Pro uses another major full-size pistol-optic mounting pattern.

You'll often see slides and adapter plates described as:

DPP footprint or DeltaPoint Pro footprint.

Glock currently groups the DeltaPoint Pro with the Vortex Defender ST/XL and EOTech EFLX on Gen6 Plate 04.

That makes Plate 04 an important factory option for shooters who aren't living in the RMR ecosystem.

Again, sharing a Glock plate tells us Glock engineered that interface plate to support those optics. It does not mean we automatically declare every dimension on every optic identical.

A direct-milled slide skips the universal adapter system and machines the slide for a specific optic interface.

Advantages can include:

• Lower optic height
• Fewer parts in the mounting stack
• Tighter optic pocket
• Better mechanical support when machined well

The trade-off is obvious:

you committed to that footprint.

Buy an RMR-cut slide and then decide you want an ACRO?

Now you're probably using a conversion plate or changing slides.

Universal systems give you flexibility. Direct cuts give you simplicity.

Sometimes an optic includes a conversion plate because the manufacturer knows the footprint isn't what most pistols are cut for.

That can work perfectly well.

But every added interface can mean:

• More height
• More screws
• More possible movement
• More tolerance stacking

We don't reject a quality adapter just because it's an adapter.

We just prefer the cleanest reliable mounting stack that gives us the optic we actually want.

This is where people get themselves into trouble.

Even when two optics use the same basic mounting family, the correct screw can change because of:

• Optic base thickness
• Plate thickness
• Slide thread depth
• Different screw thread
• Right-side internal clearance

That's why we do not have one bucket in the shop labeled:

“GLOCK OPTIC SCREWS — THEY'RE ALL THE SAME.”

For screw length, torque, threadlocker and extractor-plunger interference, use the Glock Optic Mounting Problems Guide .

How the optic mounts affects how high it sits above the slide.

A direct-milled optic usually sits lower than the same optic stacked on a thick adapter plate.

That can change:

• Iron-sight visibility
• Which backup-sight height you need
• Holster optic clearance
• How naturally the dot appears during presentation

We don't automatically chase the absolute lowest possible optic height.

But unnecessarily stacking plates higher than needed isn't usually our first choice either.

1. Identify the exact Glock model and generation.
2. Identify the exact factory or aftermarket slide cut.
3. Find the optic's actual direct-mount footprint.
4. Determine whether it mounts direct or needs a plate.
5. If a plate is needed, identify the exact plate — not just the footprint family.
6. Confirm screw thread and length for the whole setup.
7. Check optic-body width against the slide.
8. Check iron-sight and holster clearance if those matter to the build.
9. Then buy the optic.

That order prevents a lot of expensive “well shit” moments.

What footprint is Glock MOS?

Standard Gen4/Gen5 Glock MOS isn't one optic footprint. It is an adapter-plate system that supports multiple footprints.

What footprint is G43X MOS?

The standard Slimline MOS factory cut is based on the Shield RMSc footprint. Newer MOS-K variants are modified to directly support both Holosun K and RMSc families.

Will a 507K fit directly on a G43X MOS?

On MOS-K, Glock specifically supports Holosun K direct mounting. On the original standard Slimline MOS/RMSc cut, don't assume direct fit — verify the exact slide and use the appropriate interface if required.

What footprint is the EPS Carry?

Holosun currently lists EPS Carry as a direct K-footprint optic.

What footprint is the full-size EPS?

Holosun currently lists the full-size EPS as K footprint too. The body is larger, but the direct-mount interface remains K.

Is the Holosun 509T RMR footprint?

No. It uses the 509T footprint. Holosun includes an RMR-to-509T adapter plate with current 509T models.

Is Aimpoint ACRO the same as Glock A-CUT?

No. ACRO uses Aimpoint's ACRO interface. Glock A-CUT is the dedicated wedge-style mounting system used with the Aimpoint COA.

Does Gen6 use Gen5 MOS plates?

No. Gen6 has its own Optic Ready System with factory plates 02, 03 and 04 for currently supported optics.

Does the optic footprint tell me which screws to use?

Not by itself. Screw thread and length depend on the complete optic/plate/slide combination.

Glock Optic Mounting Problems
Screw length, torque, plates, extractor-plunger interference and zero shift.

Glock Compatibility Guide
Model, generation, slide and parts compatibility.

Glock Holster Fitment
Optic clearance, weapon lights, compensators and carry fitment.

Glock Cleaning & Lubrication
Optic-hardware inspection, maintenance and carry-gun checks.

Bottom Line

Don't buy a red dot because somebody said:

“Yeah, that should fit a Glock.”

Know the Glock.

Know the cut.

Know the footprint.

Know the plate.

Know the hardware.

Then mount the optic once instead of buying three plates and learning the whole damn footprint industry the expensive way.

Know the Interface Before You Buy the Glass.

The best optic in the world doesn't help much if it doesn't fit the damn slide.

This guide combines current Glock optic-system documentation, optic-manufacturer fitment information, our existing Glock compatibility work, and practical optic/build experience.

IRONKELLS ARMORY | FORGE FILES

Receipts Over Rumors.

Know the cut. Know the footprint. Stop buying the wrong damn plate.