Installing a pistol red dot: what the makers say
By the site administrator. Published September 29, 2026.
Mounting an optic is gunsmithing. This guide is the job as optic and pistol makers describe it in their own manuals, with the places they disagree left showing. It gives no torque or screw length of its own, because the right figure depends on your optic, your plate and your slide.
1. Know what you are mounting
An optic either bolts straight onto the slide’s cut, or goes on an adapter plate that bolts to the slide. That is two joints with two sets of screws instead of one. Which you have depends on your slide and your optic, and the answer for your pair is at the foot of this page and on every pistol and optic page.
2. Use the right screws, and try them first
The thread is tapped into the slide or the plate; the optic only has a clearance hole. So the slide or plate decides the thread, not the optic. SIG’s ROMEOZero manual says each set of screws in the box is meant for a specific application and using the incorrect screws can cause malfunctions or damage to the optic or the firearm SIG Sauer, ROMEOZero-ELITE operator’s manual. Both SIG manuals say to thread the screws into the mounting holes by hand before installing, to be sure they go in smoothly SIG Sauer, ROMEO-X operator’s manual; SIG Sauer, ROMEOZero-ELITE operator’s manual.
- Plate screws are not optic screws. GLOCK’s sheet says the screws removed from the cover plate should not be used to fix an adapter plate, and that the spare plate screw in the set is not recommended for fixing the optic itself GLOCK, accompanying sheet for MOS adapter plates.
- Length is a limit as well as a fit. GLOCK: before mounting the optic on the plate, make sure the optic’s screw does not protrude from the plate (the plate is 2.5 mm, 0.1 in, thick) GLOCK, accompanying sheet for MOS adapter plates. Springfield: on the Hellcat OSP, optic screws may need shortening, and must not protrude more than 0.095 in (2.4 mm) from the bottom of the sight Springfield Armory, Hellcat manual (OSP optics installation). A screw that is too long can bottom out, or reach where it must not. This site does not publish screw lengths: they depend on your stack. The build sheet has a calculator that works from your own caliper readings.
3. Clean it, and know what your maker says about threadlocker
The makers agree the surfaces should be clean and disagree on threadlocker. Read yours; this is the row that differs most.
| Maker | What its document says |
|---|---|
| SIG Sauer ROMEO-X SIG Sauer, ROMEO-X operator’s manual | Ensure the threaded holes in the mounting surface are clean, and free from debris or thread locker compound. |
| SIG Sauer ROMEOZero-ELITE SIG Sauer, ROMEOZero-ELITE operator’s manual | Wipe oil or residue from the optic cut with a clean dry cloth, then a cotton swab lightly soaked in isopropyl alcohol out of the threaded holes. Threadlocker is not mentioned. |
| GLOCK MOS plates GLOCK, accompanying sheet for MOS adapter plates | The two plate screws come with a drop of glue applied. If you often need to screw on and unscrew, apply another drop of threadlocking-type adhesive to the thread of the screws. |
| Springfield Hellcat OSP Springfield Armory, Hellcat manual (OSP optics installation) | If you choose to use thread locker, use it sparingly and on screws only. Do not apply it to the threaded holes in the OSP pocket: too much can foul the mechanism. |
This site’s build sheets list blue threadlocker as a common practice. None of the documents above says “blue”, and where yours says otherwise, yours wins.
4. Seat it, then torque it to your maker’s figure
SIG’s ROMEO-X manual says to set the optic on the mounting surface, lining up any recoil bosses with the recoil lug holes in the optic SIG Sauer, ROMEO-X operator’s manual, and both SIG manuals say to push the optic forward, toward the muzzle, while tightening SIG Sauer, ROMEO-X operator’s manual; SIG Sauer, ROMEOZero-ELITE operator’s manual. An optic that rests on its posts instead of in them puts recoil on the screws: see the lost-zero guide.
The figures below are the makers’ own, for their own optics. They are here to show how far apart the right answers are. SIG gives 28 in-lb for one optic’s M4 screws in a steel slide and 9 in-lb for another’s. Use the figure for your optic and your plate, never one from another optic or from a table.
| Document | Screw | Torque it gives |
|---|---|---|
| SIG ROMEO-X SIG Sauer, ROMEO-X operator’s manual | M3 × 0.5, SIG P365 slide only | 24 in-lb (2.71 N·m) |
| SIG ROMEO-X SIG Sauer, ROMEO-X operator’s manual | M4 × 0.7, steel slide | 28 in-lb (3.16 N·m) |
| SIG ROMEO-X SIG Sauer, ROMEO-X operator’s manual | M4 × 0.7, aluminum mount or plate | See the mount or plate maker’s specification |
| SIG ROMEOZero-ELITE SIG Sauer, ROMEOZero-ELITE operator’s manual | Screws into an optics-ready slide | 9 in-lb; warns over-torquing may cause issues with windage and elevation |
| GLOCK MOS adapter plate GLOCK, accompanying sheet for MOS adapter plates | M3 × 6 plate screws | 1.5 N·m / 13.1 in-lb, if a torque wrench is available |
SIG’s ROMEOZero manual says to re-torque each time the sight is removed and reinstalled, and after every 500 rounds fired SIG Sauer, ROMEOZero-ELITE operator’s manual. GLOCK says to verify screw tightness depending on ammunition and frequency of use GLOCK, accompanying sheet for MOS adapter plates. Use an inch-pound torque wrench. If a screw feels wrong before it reaches its figure, stop.
5. Before you fire it
- Fire it only with the cut covered. GLOCK: fire an MOS pistol only with the cover plate mounted, or an adapter plate and optical sight installed GLOCK, accompanying sheet for MOS adapter plates.
- Check that it functions. Springfield: after installing an optic, test fire to verify proper function Springfield Armory, Hellcat manual (OSP optics installation).
- Mark the screws. A paint-pen line across each screw head onto the optic or plate shows movement too small to feel. Why it matters.
- Zero it. Zeroing for the first time.
What this guide leaves to you
Screw length (yours to measure), the torque for your own optic and plate (from their makers), a threadlocker product (from your maker, if it calls for one), and any step you are not sure of (a gunsmith’s).
Sources
Read on 2026-09-29. Manuals are revised: use the current one for your own optic and plate.
- SIG Sauer, ROMEO-X operator’s manual
- SIG Sauer, ROMEOZero-ELITE operator’s manual
- GLOCK, accompanying sheet for MOS adapter plates
- Springfield Armory, Hellcat manual (OSP optics installation)