The Holosun K footprint

How to identify a Holosun K cut without a caliper

Three checks, cheapest first. Two of them are decisive and the one most people reach for is not.

1. Read the optic’s model name. Holosun is consistent enough that this settles most cases before you touch the gun. A K in the model number is the K pattern: the 407K-X2 and the 507K-X2. The word Carry in an enclosed model name means the same pattern: the EPS Carry, the Ronin EPS Carry and the SCS Carry. A C in the model number is the full size Trijicon pattern instead, as on the 507C-X2, which is why that one appears on the RMR hub and not here.
2. Turn the optic over and look at the rear of its underside. A K optic has two lug recesses toward the front and a flat rear face. An RMSc optic has four recesses, one near each corner. This is the check that cannot be faked by a box or a listing, and it is the one worth doing before the screws go anywhere near a slide.
3. Count the bosses in the slide cut, with the cover plate off. Two bosses at the front of the pocket and a bare floor behind them is the K arrangement. Four bosses, two front and two rear, is RMSc.

Counting lugs alone will not tell you K from RMR. This is the gap in the usual advice and it is worth stating plainly, because this dataset records the same two numbers for both patterns: 2 screws and 2 recoil lugs on Holosun K, and 2 screws and 2 recoil lug sockets on RMR. The discriminator between those two is size, not geometry. A K optic is a micro sight sized for a single stack carry slide; an RMR pattern optic is a full size body that will hang off the back of one. If your count comes to two and two, you have ruled out RMSc and nothing else, and the next question is which size class the part belongs to.

The size question is also where the K pattern’s parent gets people. RMSc exists at two body lengths, about 40mm and about 46mm, sharing one screw and boss layout (shieldsights.com). K lives in the 40mm class only. If you are holding something in the longer class it is not a K optic whatever the lugs say.

Pattern and dimensions

What this dataset publishes for the K pattern today:

Property	Value	Source
Mounting style	Screw-through	dataset
Mounting screws	2	dataset
Recoil lugs	2, front only, rear pair deleted	dataset
Footprint family	Holosun K	dataset
Body length class	The shorter micro class, about 40mm	dataset
Optics recorded on this pattern	5 pages covering 8 SKUs from 1 brand	dataset
Pistols cut for it directly	26 of 196, from 8 brands	dataset

Screw thread size, screw centre spacing, lug diameter and lug depth are not published here, for this pattern or for any other on this site. No manufacturer drawing carrying those figures has been read into the dataset, and the rule is to print a null rather than a guess. The three sources recorded against this footprint are third party pattern guides (opticsplanet.com, freedomgorilla.com, badassoptic.com), not a Holosun drawing. Holosun product pages are recorded against the individual optics, and they name the models; no document in this dataset publishes a dimensioned K drawing. Until one is sourced, use the screws that ship with your optic and the length the optic maker specifies for your slide.

One qualitative dimension claim is worth keeping, because it explains why the pattern exists at all: the recesses on a K body are both fewer and shallower than RMSc’s, and removing the rear pair is what allows the sealed, waterproof construction the K series is sold on. That is the reason for the modification, recorded against this footprint, and it is also why the two patterns cannot simply be treated as one.

Look-alikes that will not interchange

K against RMSc. The pair this page exists for. Same two screws, same front lug positions, rear lugs gone. The directional rule recorded here is that a K cut slide cannot directly accept an RMSc optic, and an RMSc cut slide needs an adapter, or the rear lugs filed down, to accept a K optic. Note what that means for shopping: the overlap people assume is symmetrical is not. The RMSc hub owns the 30 optic list; this page owns the 5.

K against RMR. Two screws and two lugs on both, as above, and no relation beyond that. The RMR hub carries 33 optics against 5 here, and 7 pistols cut for it directly against 26 here. If you are comparing patterns to pick a gun rather than an optic, those two numbers are the trade in one line: RMR has the deeper optic bench, K is cut into more slides in this dataset.

K against the full size Holosun EPS. Until 2026-10-04 the hub description above said the K pattern was used by the 407K, the 507K, the EPS and the EPS Carry. The EPS in that list was doing real damage, because the full size EPS is tracked here as its own footprint: the K base with additional front sockets, four lug positions rather than two (holosun.com). No pistol in this dataset is cut for it. The description now names the five optic rows this dataset actually files under K, the 407K-X2, the 507K-X2, the EPS Carry, the Ronin EPS Carry and the SCS Carry, so the paragraph above and the table below agree. The distinction is still worth reading twice, because the two enclosed models are one word apart and mount differently.

K against the Holosun EPS Core. Same enclosed line, same three letters, a different mount. The EPS Core is cut for RMSc (holosun.com), not for K. If you want a sealed emitter and your slide is RMSc only, this is the model to look at rather than the EPS Carry.

K against the Holosun 509T and the dovetail patterns. The 509T clamps rather than screwing through, as does ACRO. If the optic has no through holes in its base at all, neither this pattern nor RMSc is the answer. The Docter pattern uses two screws and four lugs like RMSc but a different body again.

K against a plate system. Glock MOS and the other 14 plate systems in this dataset are not footprints. A plate drops into the slide and its top face carries a footprint. Only one of those 15 systems is recorded here as presenting K, which is the subject of the plate section below.

What this dataset records for K, and what it inherited from RMSc

This is the part a buyer should read before trusting any of the counts on this page, including ours.

None of the 5 K optic pages is flagged verified. 48 of the 100 optic pages in this dataset carry a verified flag, meaning the maker’s own page, or two independent retailer pages, was read and the sentence stating the footprint is recorded against the row. Zero of those 48 are K optics. Three of the five do cite a holosun.com product page for the model; the two enclosed EPS Carry rows rest on a retailer mounting guide (opticsforce.com) instead. That is sourced research, and it is not the same thing as verified.

The 26 pistol rows are sourced for their RMSc cut, not for their K cut. Every one of the 26 was recorded from a page describing the slide as RMSc cut, and the K entry sits alongside it. 18 of the 26 rest on a single list titled RMSc footprint compatible handguns (swampfoxoptics.com). Not one of the 26 cites a holosun.com page, and none cites a document about the K pattern. The dual listing is a defensible reading of how micro slides are machined, and it is still an inference rather than a cited K fitment.

There is a visible consequence, and leaving it unsaid would be worse than printing it. The footprint record says an RMSc cut needs an adapter to take a K optic, while all 26 pistols listed above are recorded as RMSc cut and as taking K directly. Both statements cannot be strictly true of the same slide. The reconciliation that fits the hardware is that these micro slides are cut so that both bodies seat, which is exactly why they are sold as taking a RomeoZero and a 507K alike, and the honest version is that this dataset has not sourced that slide by slide. So: use the 26 as a strong shortlist, and confirm your specific model and generation on the maker’s page before you buy. Slide cuts change between variants of one name more often than model pages admit.

One pair of rows disagrees with itself. The dataset holds a P365 XL recorded as RMSc only, reaching 30 optics, and a P365XL recorded as RMSc and K, reaching 35. Those look like one pistol entered twice from two sources, and the pistol list above contains the second. Treat the 35 figure as the one to check and not as two different guns.

How a plate gets you to Holosun K

Exactly one pistol here reaches a K optic without a K cut: the Springfield XD-M Elite OSP, through the K variant of the Springfield XD OSP optic plate. That slide has no direct fit optic at all. Everything it mounts, it mounts through a plate, and across five plates it reaches 89 optics: 33 on the RMR plate, 30 on RMSc, 15 on DeltaPoint Pro, 6 on Docter and 5 on K. The system’s own page is the Springfield XD OSP hub.

In words, a plate path works like this. The slide is milled for a proprietary pocket that is not a footprint at all. A plate drops into that pocket and its top face carries a real footprint. Buy the plate that presents K and the slide behaves, for optic buying purposes, like a K slide. The plate table for each system lives on that system’s own hub, never here.

One path is almost certainly an undercount, and here is the evidence we have not acted on. Four plate systems in this dataset were built from C&H Precision compatibility pages, and each of those pages lists a plate for the Holosun 407k and 507k alongside the ones for the full size patterns: FN 509 (chpws.com), HK VP9 OR (chpws.com), CZ P-10 OR (chpws.com) and S&W M&P CORE (chpws.com). Those four systems carry 39 pistols between them, and this dataset records no K presenting plate on any of them: their plate rows were recorded as RMR, RMSc, DeltaPoint Pro and ACRO. So the single plate path on this page is what we publish, not a claim that only one exists. Until the rows are rebuilt and re-exported, 1 is the number this site will stand behind and 39 pistols are the size of the question.

A plate also costs you height above the bore and one more interface that can loosen. If your slide is cut for K directly, that is the better mount.

How to choose a Holosun K optic

No prices on this page and no rankings the data can support. What the data does support:

• Your list is 35, not 5. All 26 K cut pistols here are recorded as taking RMSc optics directly as well, so the shortlist on any of them is 35 of the 100 optic pages in this dataset: the 5 here plus the 30 on RMSc, with no overlap. A slide cut for RMSc alone reaches 30. In this dataset the K cut buys 5 extra optics, not a separate shopping list.
• Brand depth comes from the RMSc half. All 5 K optics are Holosun. Across the 35 a K cut slide reaches 12 of the 16 optic brands in this dataset, and every one of those 12 is reachable through the RMSc half alone. The K half contributes Holosun and nothing else. If brand choice matters to you, the K pattern is not where you will find it.
• Decide sealed or open first. This is the reason most buyers end up looking at a K optic. 3 of the 5 K optics here are enclosed: the EPS Carry, the Ronin EPS Carry and the SCS Carry. Across the full 35 there are 11 enclosed options of the 27 in the dataset, so 8 of your enclosed choices are RMSc parts, among them the EPS Core. Sealed matters most for a gun carried daily in a holster, where lint and rain reach an open emitter.
• If your slide is RMSc only, the EPS Carry is the cheapest route to K. Holosun’s EPS mounting documentation records the EPS Carry as shipping with an RMSc adapter plate in the box, and the full size EPS with an RMR plate (opticsforce.com, holosun.com). That is the one case in this dataset where the adapter the footprint record says you need is already paid for. Confirm the in box contents on the listing you are buying from, because kit contents change without the pattern changing.
• Check the optic page, not the brand. Each optic page here lists the pistols it fits and the source for that claim. Start with the 507K-X2 and the EPS Carry if you want the two most widely stocked shapes.
• A K slide is a narrow slide, and the numbers say so. 35 of 100 optic pages is well under the median: across all 196 pistols here the median reach is 83, because plate system guns can present four or five patterns and a dual cut micro slide presents two. 58 pistols reach fewer optics than a K cut pistol and 112 reach more. That is the trade a carry sized slide makes, not a fault.

Nothing on this site is verified against a physical sample. 48 of the 100 optic pages carry a verified flag and none of the five here is among them, so for this pattern specifically the manufacturer’s own listing is the higher authority. Treat these fits as sourced research, then confirm against your own slide.

Where to go next

• The full chart: all optic footprints and plate systems.
• The long form article this hub owns: Holosun K footprint vs RMSc.
• The parent pattern and its 30 optics: the RMSc footprint guide.
• When your slide is not cut for what you want: do you need an adapter plate?
• The largest K cut family in the dataset: SIG P365 red dot compatibility.
• Popular K cut slides: SIG P365XL, Ruger MAX-9, Taurus GX4 TORO, Canik METE MC9, S&W Equalizer, FN Reflex MRD.