Holosun 407K Glock MOS Plate Compatibility Guide

The Holosun 407K does not mount directly to a standard Glock MOS slide. The pistol's factory mounting interface and the optic's mounting footprint are different—a compatible adapter plate sits between them. For standard Glock MOS pistols, the StoneIron Defense SID-2259 is listed as compatible with the Holosun 407K, 507K, EPS, and EPS Carry.

Two models are explicitly excluded by StoneIron Defense's product documentation: the Glock 43X MOS and Glock 48 MOS. Those are Slimline models with a different slide configuration, addressed separately below.

Does the Holosun 407K Fit a Glock MOS Pistol?

Not without an adapter plate.

The Holosun 407K X2 uses Holosun's K-series mounting footprint—a compact two-screw pattern derived from the Shield RMSc design. Standard Glock MOS slides are machined with Glock's proprietary MOS cutout, which is not the same as the K footprint. No standard Glock MOS adapter plate covers the K footprint directly; Glock's own documentation confirms its included plate covers Trijicon, Ameriglo, and Holosun optics except the 509 series—not K-footprint models.

An aftermarket adapter plate is therefore required. The plate's underside fits the Glock MOS cutout on the slide; its top face presents the K-footprint surface the optic mounts to.

The same requirement applies to the Holosun 507K X2. It uses an identical K footprint to the 407K, and the same adapter plate serves both.

Which Glock MOS Plate Fits the Holosun 407K and 507K?

The StoneIron Defense SID-2259 is designed for this application. It is listed by StoneIron Defense as compatible with the Holosun 407K, 507K, EPS, and EPS Carry on standard Glock MOS pistols.

SID-2259 Product Specifications

What's in the box:

• 1× Glock MOS K-Footprint Optic Plate
• Precision Fit Plate Mounting Screws
• Optic Mounting Screws (model-specific)
• T10 Torx Installation Tool
• M3 Allen Key

Exact screw thread specifications and torque values are not published on the product page. StoneIron Defense recommends installation by a qualified gunsmith. For installation-specific questions, contact them at info@stoneirondefense.com.

The plate is CNC machined from 4140 billet steel, heat-treated to 35–42 HRC, and finished in black nitride. These are StoneIron Defense's published material specifications; no independent durability comparison is implied.

Glock models listed as compatible:

• Glock 17 MOS
• Glock 19 MOS
• Glock 22 MOS
• Glock 23 MOS
• Glock 34 MOS
• Glock 35 MOS
• Glock 41 MOS
• Glock 45 MOS

This list reflects what StoneIron Defense has published on the product page. It does not necessarily represent every standard Glock MOS configuration; if your model is not listed, confirm with StoneIron Defense before ordering.

Supported Holosun Optics

StoneIron Defense lists all four of the following optics as compatible with SID-2259:

• Holosun 407K (original K footprint)
• Holosun 507K (original K footprint)
• Holosun EPS (extended K footprint)
• Holosun EPS Carry (extended K footprint)

The 407K and 507K use Holosun's original K footprint. The EPS and EPS Carry use a related but distinct extended K footprint, which Holosun describes as backward compatible with original K accessories. According to Holosun's footprint documentation, a plate or slide cut designed for the original K footprint (407K/507K) will accept an EPS or EPS Carry—but a plate made specifically for the EPS may not accept a 407K or 507K. Because SID-2259 is designed around the original K footprint, it supports all four optics through this backward compatibility.

Do not assume that all four optics have identical mounting geometry. The EPS and EPS Carry have four additional holes compared to the original K pattern, which is what creates the extended designation.

Glock MOS and Holosun K Footprint Compatibility Chart

"Listed by StoneIron Defense" reflects published product documentation, not independently conducted physical testing of every combination. "Excluded" is taken verbatim from the SID-2259 product page.

Does SID-2259 Fit Glock 43X MOS or Glock 48 MOS?

SID-2259 does not fit the Glock 43X MOS or Glock 48 MOS. StoneIron Defense's product page states this explicitly: "Not designed for Glock 43X MOS or Glock 48 MOS."

This is a limitation of SID-2259, not a universal restriction on those pistols.

Standard MOS vs. Slimline MOS:

The Glock 43X MOS and 48 MOS are Slimline models. Their slides are dimensioned differently than standard double-stack MOS frames like the Glock 17 or 19. Standard Glock MOS adapter plates—including SID-2259—are designed around the standard MOS slide cutout geometry. That geometry does not carry over to Slimline slides.

What about Holosun 407K and 507K on a 43X or 48? Those optics can still be mounted on these pistols, but through a different route:

• Existing Slimline MOS (older RMSc-cut slides): The Glock 43X MOS and 48 MOS were originally released with an RMSc-based slide cut. Because the K footprint shares the same screw spacing as the RMSc, an RMSc-to-K adapter plate can be used to mount a 407K or 507K. SID-2259 is not that plate—it is designed for the standard MOS interface, not the Slimline interface.
• Newer Slimline MOS-K slides: As of late 2025, Glock began updating some Slimline models to what it calls the MOS-K cut. Pistols with this configuration are identified by "MOSK" in the item number on the case sticker. An MOS-K slide accepts K-footprint optics directly, without any adapter plate. If your Glock 43X or 48 carries the MOS-K designation, the 407K and 507K can mount directly to the slide—no plate required, and SID-2259 would not apply regardless.

To identify your slide variant, check the item number sticker on the grip handle of your pistol case, as referenced in Glock's official MOS documentation. If the identifier includes "MOSK," you have the K-cut slide.

Are Holosun EPS and EPS Carry Compatible with SID-2259?

StoneIron Defense lists both the Holosun EPS and Holosun EPS Carry as compatible with SID-2259.

The technical basis for this is Holosun's extended K footprint compatibility. The EPS and EPS Carry use an extended K footprint—a variation of the original K pattern that includes four additional mounting holes. Holosun's footprint documentation states that EPS accessories are backward compatible with original K accessories, meaning an original K-footprint plate (designed for the 407K and 507K) will correctly accept EPS and EPS Carry optics.

The practical result: SID-2259, designed around the original K footprint, supports all four optics per StoneIron Defense's published documentation.

Important distinction from Holosun's own Glock MOS adapter: Holosun's official Glock MOS adapter (HS-MOUNT-407K-507K-GLOCK-MOS) explicitly states "Only compatible with the 407K / 507K models"—it does not list EPS or EPS Carry as supported. StoneIron Defense's SID-2259 specifically covers all four optics.

If you are running an EPS or EPS Carry on a standard Glock MOS pistol, verify compatibility directly with StoneIron Defense before ordering, as the EPS and EPS Carry represent an extended K specification.

What Is the Difference Between Glock MOS, K, and RMSC Footprints?

These three terms describe different things and belong to different parts of the mounting chain.

Glock MOS is the pistol's slide-top interface—the machined cutout that accepts adapter plates. It is not an optic footprint; it describes how the plate sits in the slide.

The Holosun K footprint is the optic's mounting interface—the pattern of locating posts and screw holes on the bottom of the 407K and 507K. It is a modification of the Shield RMSc pattern, with the two rear locating posts removed and shorter front posts. The K footprint is not the same as the RMSc footprint; they are related but distinct.

The extended K footprint is used by the EPS and EPS Carry. It retains full backward compatibility with original K accessories while adding four additional holes.

The RMR footprint is Trijicon's separate standard, used by the RMR, SRO, and Holosun's own 407C/507C/508T. It is not the same as the K footprint, and an RMR-footprint plate will not correctly accommodate a K-footprint optic.

The mounting chain for a Glock 19 MOS with a Holosun 407K therefore has three components: the optic (K footprint on its bottom) → the adapter plate (K footprint on top, Glock MOS cutout on bottom) → the slide (Glock MOS cutout machined in).

For RMR-footprint optics on the same standard Glock MOS pistols, StoneIron Defense's separate Glock MOS RMR optic plate (SID-2258) covers the Trijicon RMR, Trijicon SRO, Holosun 407C, 507C, and 508T. That is a different product from SID-2259 and serves a different optic footprint.

SID-2259 vs. Holosun's Glock MOS Adapter

Holosun produces its own Glock MOS adapter for the 407K and 507K (model: HS-MOUNT-407K-507K-GLOCK-MOS), which provides a natural point of comparison.

The most significant functional difference: Holosun's own adapter explicitly supports only the 407K and 507K, while SID-2259 extends listed compatibility to the EPS and EPS Carry. Buyers running an EPS or EPS Carry on a standard Glock MOS pistol should factor that distinction into their decision.

The other substantive difference is material: SID-2259 uses 4140 billet steel at 35–42 HRC; the Holosun adapter uses aluminum. No independent comparative testing is documented here—these are the manufacturers' published specifications.

What Should You Check Before Ordering a Glock MOS K-Footprint Plate?

Before purchasing an adapter plate, verify the following details:

• 1. Exact Glock model: Not just the frame size—confirm the full model designation.
• 2. MOS configuration: Determine whether your pistol has a standard MOS configuration or a Slimline MOS configuration. Standard MOS models include the Glock 17, 19, 22, 23, 34, 35, 41, and 45. Slimline MOS models include the Glock 43X MOS and 48 MOS.
• 3. Slimline MOS-K identification: If you own a Glock 43X MOS or 48 MOS, check the item number sticker on the pistol case handle. A designation including "MOSK" indicates the newer K-cut slide that accepts K-footprint optics directly. If your pistol has that designation, you don't need an adapter plate, and SID-2259 isn't applicable.
• 4. Exact optic model and generation: The current 407K and 507K are the X2 series. Confirm your optic's footprint matches the K or extended K standard.
• 5. Which plate you need: SID-2259 covers K-footprint optics (407K, 507K, EPS, EPS Carry). If you are mounting an RMR-footprint optic (Trijicon RMR, Holosun 507C, etc.), you need the SID-2258 instead.
• 6. Included hardware: SID-2259 includes plate mounting screws, optic mounting screws, a T10 Torx tool, and an M3 Allen key. Verify all hardware is present before beginning installation.
• 7. Installation guidance: Exact torque values are not published. StoneIron Defense recommends that a qualified gunsmith perform the installation. Contact info@stoneirondefense.com for manufacturer-specific guidance.

For a broader overview of which optic plates cover which footprints, see StoneIron Defense's Glock MOS optic plate compatibility chart.

Frequently Asked Questions

Can Holosun 407K fit a Glock 19 MOS?

Yes, with the SID-2259. The Glock 19 MOS is on StoneIron Defense's listed compatibility for SID-2259. The 407K does not mount to the slide directly; the adapter plate is required.

Does Holosun 507K use the same plate as the 407K?

Yes. The 507K and 407K use the same original K footprint and are both listed as compatible with SID-2259. The only difference between the two optics is the reticle configuration.

Does SID-2259 support Holosun EPS and EPS Carry?

Yes, per StoneIron Defense's published product documentation. The EPS and EPS Carry use the extended K footprint, which Holosun documents as backward compatible with original K accessories such as SID-2259. If you are specifically installing an EPS or EPS Carry, confirm with StoneIron Defense before ordering.

Does SID-2259 fit Glock 43X MOS?

No. The SID-2259 product page explicitly states it is not designed for the Glock 43X MOS. The 43X MOS is a Slimline model with a different slide configuration. This is a limitation of SID-2259 specifically, not of the 43X platform.

Does SID-2259 fit the Glock 48 MOS?

No. Same exclusion applies. The Glock 48 MOS is a Slimline model and is explicitly excluded from SID-2259 compatibility.

Is Holosun K footprint the same as RMR?

No. The K footprint is derived from the Shield RMSc pattern. It differs from the Trijicon RMR footprint in the number and position of locating posts. An RMR-footprint plate will not correctly seat a K-footprint optic.

Does a standard Glock MOS need an adapter plate for Holosun 407K?

Yes. No standard Glock MOS adapter plate includes the K footprint. An aftermarket K-footprint plate—such as SID-2259—is required for all standard MOS models.

How do I identify whether my Glock has a standard MOS or MOS-K slide?

Check the item number sticker on the grip handle of your pistol case. Standard MOS configurations are labelled "MOS" in the item number. The newer Slimline K-cut configuration is labelled "MOSK." Glock's official MOS documentation explains this identification method.

What hardware comes with SID-2259?

The SID-2259 includes plate mounting screws, optic mounting screws (model-specific), a T10 Torx installation tool, and an M3 Allen key.

Where can I find the correct installation specifications?

Exact torque values and screw thread dimensions are not published on the SID-2259 product page. Contact StoneIron Defense at info@stoneirondefense.com or consult a qualified gunsmith for specific installation guidance.

Final Compatibility Recommendation

If your pistol is a standard Glock MOS model—Glock 17, 19, 22, 23, 34, 35, 41, or 45 MOS—and you are mounting a Holosun 407K, 507K, EPS, or EPS Carry, the StoneIron Defense SID-2259 is listed by the manufacturer as a compatible adapter plate.

If your pistol is a Glock 43X MOS or Glock 48 MOS, SID-2259 is not designed for your slide. Those models require a Slimline-specific mounting solution. If your 43X or 48 carries the newer MOS-K slide cut (identified by "MOSK" in the item number), you may not need any adapter plate at all—check Glock's official documentation first.

For RMR-footprint optics on the same standard Glock MOS pistols, see the Glock MOS RMR optic plate (SID-2258). That is a separate product serving a separate footprint family.