Do You Actually Need an Adapter Plate?

Start here, because a meaningful share of adapter plates get bought by people who never needed one. Across 117 customer returns on our own AC311 adapter plate, at least 9 of the 77 written comments say some version of the same thing: "I did not need adapter, optic fit without it." One buyer returned an unopened package with the note "My slide didn’t need the spacer." The reason is simple — they bought a true RMSc-footprint optic, and the 43X MOS slide is already cut for it.

Find your optic in the table below before you buy anything:

A note on that return data: those percentages describe the mix of written return comments, not a failure rate. Customers who are happy rarely write anything, so the sample is self-selected. It is useful for showing which misunderstandings are common, not how often the part fails.

If your question is really "which red dot should I put on this pistol," that is a different decision — we cover the optics themselves, including battery life, window size and price, in our guide to which red dots fit the Glock 43X MOS. This page stays focused on the mounting interface.

What Are the 3 Red Dot Footprints for Glock 43X MOS?

The single biggest source of confusion when shopping for a Glock 43X adapter plate is mixing up the three distinct mounting footprints. Each footprint has different screw spacing, recoil lug positions, and physical dimensions. Using the wrong plate means the optic either will not bolt on at all, or worse, bolts on loosely and shifts zero under recoil.

Critical distinction: The RMRcc footprint is NOT the same as the RMSc footprint, even though both are “compact.” A plate made for Holosun 507K (RMSc) will not accept a Trijicon RMRcc, and vice versa. Always verify the specific footprint listed on the plate before purchasing.

Why Your Holosun Sits Proud: The 0.011" Problem

This is the part almost every buying guide skips, and it is the reason the internet cannot agree on whether a Holosun 507K "fits" a Glock 43X MOS. Both answers you will find are half right.

The screws do line up. Holosun’s K-series and the Shield RMSc pattern share the same bolt spacing — roughly 0.92 inches between screw centers, compared with 0.83 inches on a full-size RMR. That is why some sources say the K-series is not a separate footprint at all.

The locating posts do not. A standard RMSc interface uses four recoil lugs — two front, two rear. Holosun’s K-series has recesses for the two front posts only and nothing at the rear; Holosun removed the rear pockets to seal the housing, which is what makes the K-series the only waterproof optic in its size class. The front recesses are also shallower than the slide’s posts are tall.

A shooter on the Primary & Secondary forum measured the mismatch directly:

"the 507k does not have the recesses in the rear for the posts, and the front recesses are shorter than the Glock posts."

The numbers behind that sentence: the Holosun front recesses run about 0.029 inch deep against slide posts standing roughly 0.040 inch tall. That leaves 0.011 inch of interference at the front, while the two rear posts have nowhere to go at all. The optic ends up bridged on its posts at both ends instead of bedded flat on the slide.

Why this matters beyond cosmetics. Those posts are not alignment aids — they are the structural feature that absorbs recoil shear so the screws only have to supply clamping force. An optic bridged on mismatched posts loads its screws in shear on every shot. That is the mechanism behind the most common complaint that follows a "it looked fine when I torqued it" install: the dot loses zero, then the screws back out.

You have two legitimate ways to resolve it, and one that costs you more than it saves:

• Adapter plate (reversible, ~$35–65). The plate bolts to the slide’s RMSc posts and presents K-series geometry on its top face. Nothing about the pistol is permanently changed.
• Professional slide milling (permanent, ~$150–300). Shops such as JagerWerks and Wager Machine Works remove the rear posts and shorten the front pair so a K-series optic beds directly. Lowest possible mount, but irreversible.
• Filing the posts down yourself — not recommended. It is mechanically possible, and the Primary & Secondary thread includes a follow-up from a shooter who did exactly that and then fought screws working loose under live fire. Once the posts are gone, the screws carry the recoil shear alone.

Height is the honest trade-off with any plate. It is also the second-most-common complaint we see in our own return comments — buyers who mounted successfully but wrote "can’t see iron sights." If co-witness matters to you, plate thickness is the spec to compare, not material.

Which RMSc Adapter Plates Work Best? (Holosun 407K/507K)

The RMSc footprint is the most popular choice for the Glock 43X MOS because Holosun's K-series optics dominate the compact red dot market. The Holosun 507K ($290) offers the best balance of features, battery life (50,000 hours), and reliability for concealed carry.

For RMSc mounting, three plates stand out:

The AltitudeCraft plate uses Grade 5 titanium (6Al-4V alloy, 120,000 PSI tensile strength) CNC-machined to ±0.001" tolerance. At 0.058" thick, it is the thinnest option available, which provides the best co-witness with suppressor-height iron sights. It also fits the Glock 48 MOS and Springfield Hellcat OSP.

Disclosure: AltitudeCraft is our product. The CHPWS V4 and FCD OPF-G are excellent alternatives — if steel durability or premium aluminum matters more to your use case, those are strong choices we recommend without hesitation.

Which Adapter Plate Fits the Trijicon RMRcc?

The Trijicon RMRcc (compact) was specifically designed for slimline pistols like the Glock 43X. Unlike the full-size RMR, the RMRcc fits the narrow slide width — but it uses its own unique footprint that is not compatible with RMSc plates.

Dedicated RMRcc plates for the 43X MOS:

The Trijicon RMRcc ($500–600) is a premium optic that commands a premium mounting solution. According to GlockTalk forums, the CHPWS V4 RMRcc plate is the most recommended aftermarket option, though Trijicon's own AC32126 plate is the simplest plug-and-play solution with the included sealing plate.

Important: The RMRcc is physically longer than RMSc optics, which means the adapter plate necessarily raises the mounting surface slightly. This is normal — the trade-off is access to Trijicon's legendary durability and battery life.

Can You Mount a Full-Size RMR on Glock 43X MOS?

No — not with just an adapter plate. The standard Trijicon RMR (and SRO) is physically too wide for the Glock 43X's narrow slide. The optic body overhangs both sides of the slide, creating an unsafe mounting condition where the optic can catch on holsters or clothing.

If you specifically want a full-size RMR on your 43X, you need custom slide milling from a gunsmith who specializes in optic cuts. This typically costs $150–300 and involves cutting a deeper pocket into the slide, lowering the optic closer to the bore axis. However, this permanently modifies your slide and is irreversible.

For most Glock 43X owners, the Holosun 507K (RMSc footprint, $290) or Trijicon RMRcc ($500–600) are the practical choices that mount via adapter plate without permanent modifications.

How Do the Top Adapter Plates Compare?

Here is a consolidated comparison of all adapter plates available for the Glock 43X MOS across both RMSc and RMRcc footprints.

Decision guide: If you own a Holosun 407K or 507K, get an RMSc plate. If you own a Trijicon RMRcc, get a dedicated RMRcc plate. Do not mix these — the screw holes and recoil lug positions are different between the two footprints.

How to Install an Adapter Plate on Glock 43X MOS (Step-by-Step)

The installation process is identical for both RMSc and RMRcc plates. This takes 10–15 minutes with basic tools.

Tools Required

• T10 Torx driver
• Blue Loctite 242 (medium-strength threadlocker)
• Torque wrench calibrated to inch-pounds
• Isopropyl alcohol + lint-free cloth

Step 1: Safety and Prep

Remove magazine, clear chamber, field-strip the slide from the frame. Clean the MOS mounting surface with isopropyl alcohol to remove oil and debris.

Step 2: Remove Factory Cover Plate

Unscrew the two factory screws holding the Glock cover plate. Set these aside — use the screws included with your aftermarket plate, not factory hardware.

Step 3: Dry Fit

Place adapter plate onto slide without threadlocker. Verify: recoil lugs align, screw holes match, plate sits flat. Place optic on top to confirm fitment. If anything rocks or gaps appear, stop and verify you have the correct plate for your footprint.

Step 4: Mount Plate

Apply one drop of Blue Loctite 242 per screw. Seat plate with lugs engaged. Torque to 15–18 inch-pounds. Do not exceed 20 inch-pounds — the slide's threaded inserts can strip.

Step 5: Mount Optic

Apply Loctite to optic screws. Alternating-pattern tighten to 12–15 inch-pounds for Holosun, or 16 inch-pounds for Trijicon RMRcc (per Trijicon specification).

Step 6: Cure and Verify

Wait 24 hours for full Loctite cure. Reassemble, function-check the slide without ammunition. After your first 50–100 round range session, re-check torque on all screws.

What Are the Most Common RMR Plate Mistakes?

Mistake #1: Buying an RMSc Plate for an RMRcc Optic (or Vice Versa)

The RMSc and RMRcc footprints look similar in photos but have different screw spacing. If your optic is a Trijicon RMRcc, you need a plate specifically marked “RMRcc.” If it is a Holosun 407K or 507K, you need an “RMSc” plate. Mixing these up is the #1 return reason at most retailers.

Mistake #2: Trying to Mount a Full-Size RMR Without Milling

The standard Trijicon RMR is 1.77" long and 1.13" wide. The Glock 43X slide is only ~0.87" wide. No adapter plate can make a full-size RMR fit safely on this slide. If forums or sellers claim otherwise, they are incorrect.

Mistake #3: Using a Standard MOS Plate Instead of Slim MOS

Adapter plates for Glock 17/19/45 MOS (standard MOS pattern) have wider screw spacing than Glock 43X/48 (Slim MOS pattern). Always confirm the plate lists “43X/48 MOS” specifically. See our detailed Holosun adapter plate guide for the Slim MOS vs Standard MOS comparison table.

Mistake #4: Skipping Loctite

Without Blue Loctite 242, mounting screws loosen within 200–500 rounds of 9mm recoil (source: Brian Enos Forums). Never use red (permanent) Loctite — blue (medium) allows future serviceability.

Our Verdict: Best Plate by Optic Choice

Frequently Asked Questions

Does the Glock 43X MOS need an adapter plate for the Holosun 507K?

Yes. The 43X MOS slide is cut in the Shield RMSc pattern with four locating posts, and the Holosun 507K has recesses for only the two front posts — which are themselves about 0.011 inch too shallow for the slide’s posts. Without a plate the optic sits proud at both ends, so the mounting screws end up carrying recoil shear that the posts are supposed to absorb. An adapter plate or professional slide milling is required.

What optic footprint is the Glock 43X MOS?

Shield RMSc. Glock cut the 43X MOS and 48 MOS slides for the RMSc pattern: two screws on roughly 0.92 inch centers with four locating posts, two forward and two aft. Optics built to true RMSc spec — Shield RMSc and SMSc, SIG Romeo Zero, Swampfox Sentinel — mount directly to the slide with no plate.

Why do some people say the Holosun K-series fits the RMSc footprint and others say it does not?

Because both statements describe different halves of the interface. The K-series matches the RMSc screw spacing exactly, so by bolt pattern it is the same footprint. It does not match the post geometry: Holosun deleted the rear post recesses to make the optic waterproof. Sources looking at screw spacing report compatibility; sources trying to actually seat the optic report interference. Both are accurate and neither is complete.

Does the Trijicon RMR fit the Glock 43X MOS with an adapter plate?

The full-size Trijicon RMR does not fit the Glock 43X MOS with any adapter plate. The optic is physically too wide for the narrow 43X slide. The Trijicon RMRcc (compact version) does fit with a dedicated RMRcc adapter plate such as the Trijicon AC32126 or CHPWS V4 RMRcc.

What is the difference between RMSc and RMRcc footprints?

RMSc (Shield) and RMRcc (Trijicon) are two different mounting patterns with different screw spacing and recoil lug positions. RMSc plates fit Holosun 407K, 507K, and EPS Carry. RMRcc plates fit only the Trijicon RMRcc. These plates are not interchangeable.

Can I use a Glock 17 MOS adapter plate on the 43X?

No. The Glock 43X uses the Slim MOS pattern with narrower screw spacing than the standard MOS pattern on Glock 17, 19, and 45 models. Standard MOS plates physically will not fit the 43X slide.

What torque specs should I use for the adapter plate?

Plate-to-slide screws: 15–18 inch-pounds. Optic-to-plate screws: 12–15 inch-pounds for Holosun, 16 inch-pounds for Trijicon RMRcc. Always use Blue Loctite 242 and a calibrated torque driver.

Does the AltitudeCraft plate work with the Trijicon RMRcc?

No. The AltitudeCraft plate is designed for the RMSc footprint (Holosun 407K, 507K, EPS Carry). For the Trijicon RMRcc, use the Trijicon AC32126 plate or CHPWS V4 RMRcc plate.

Is the Holosun 507K or Trijicon RMRcc better for Glock 43X?

The Holosun 507K ($290) offers better value with multi-reticle system and 50,000-hour battery life. The Trijicon RMRcc ($500–600) offers superior durability with a proven military/law enforcement track record. For concealed carry on a budget, the 507K wins. For duty use where absolute reliability justifies the premium, the RMRcc wins.