How to Choose the Right Red Dot Mounting Screws: Complete Guide to Size, Length & Compatibility

Mounting a red dot sight may seem simple: place the optic on the slide or mounting plate, install the screws, and tighten everything down. In reality, choosing the right red dot mounting screws is one of the most important parts of the installation process.

The wrong red dot screws can create problems ranging from poor fit to damaged threads. Screws that are too long may bottom out or interfere with the mounting system, while screws that are too short may not provide sufficient thread engagement. Using the wrong diameter or thread type can also damage the mounting holes.

That is why selecting the right red dot screw size, red dot screw length, and red dot screw compatibility matters just as much as choosing the optic itself.

This guide explains how to choose the right screws for pistol optics and other red dot mounting applications. We will cover screw size, length, compatibility, common mounting problems, replacement screws, footprints, and practical troubleshooting.

Important: Always follow the optic, firearm, slide, and mounting plate manufacturer's installation instructions, including the specified screw type and torque requirements. Do not force a screw that does not thread smoothly.

Quick Guide: How to Choose the Right Red Dot Screws

Before installing a red dot, check these six factors:

1. Thread diameter – What screw diameter does your mounting system require?
2. Thread type/pitch – Does the thread match the mounting hole?
3. Screw length – Is the screw long enough without being too long?
4. Screw head style – Does the head sit correctly in the optic or plate?
5. Mounting configuration – Direct mount, adapter plate, or other system?
6. Exact compatibility – Does the screw match your specific optic and mounting setup?

A useful way to think about the process is:

Optic → Footprint → Mounting Method → Thread Size → Screw Length → Head Style → Manufacturer Specifications

1. Red Dot Screw Size: Start With the Correct Thread

The first step in choosing optic mounting screws is identifying the correct screw size.

When people search for red dot screw size, they may be referring to several different measurements:

• Thread diameter
• Thread pitch
• Metric or imperial designation
• Screw length
• Head diameter

These are not interchangeable.

For example, two screws may appear similar in diameter but use different thread standards. A screw that looks like it should fit should never be forced into a threaded hole.

Common red dot mounting hardware may include thread sizes such as:

• M3
• M3.5
• M4
• #4-40
• #6-32
• #6-40
• #6-48

The correct option depends on the exact mounting system.

Metric vs Imperial Red Dot Screws

One common source of confusion is mixing metric and imperial screw systems.

For example:

• M3 is a metric designation.
• #4-40 is an imperial thread designation.
• #6-32 and #6-40 have the same nominal number size but different thread counts.

This is why matching only the approximate diameter is not enough.

Best Practice

If you do not know the required thread:

• Check the optic manufacturer's instructions.
• Check the firearm or slide manufacturer's specifications.
• Check the mounting plate manufacturer's documentation.
• Compare the original screws if they are known to be correct.
• Test fit gently by hand—never force the threads.

If a screw does not engage smoothly, stop and verify the specification.

2. Red Dot Screw Length: Why a Few Millimeters Matter

Choosing the correct red dot screw length is just as important as selecting the correct thread.

A screw must pass through the optic or mounting plate and still provide appropriate engagement with the threaded mounting hole.

However, the longest screw is not automatically the best screw.

The mounting stack can include:

Screw Head → Optic → Mounting Plate (if used) → Slide/Mount → Threaded Hole

Each layer affects the required screw length.

Red Dot Screws Too Long

One of the most common installation problems is using red dot screws too long for the specific mounting configuration.

A screw may be too long when:

• It extends beyond the available threaded depth.
• It bottoms out before the optic is properly secured.
• It is designed for a different mounting plate thickness.
• It was selected for a different optic model or mounting configuration.

A screw that reaches the bottom of a hole before clamping the optic correctly can create the false impression that the installation is secure.

For this reason, never assume that a screw is correct simply because it threads into the hole.

Red Dot Screws Too Short

Red dot screws too short can create the opposite problem.

If a screw does not provide sufficient engagement for the intended mounting system, the assembly may not be secured as designed.

This can happen when:

• A mounting plate adds additional thickness.
• The optic is taller than the previous model.
• Replacement screws were selected based only on thread size.
• The original screws are lost and the wrong length is chosen.

The correct red dot screw length must therefore account for the entire mounting stack.

Important Tip

Thread size and screw length are two separate decisions.

A screw can have the correct thread but the wrong length.

3. Red Dot Screw Compatibility: Footprint Alone Is Not Enough

Many buyers assume that if an optic uses the same red dot footprint, the mounting screws must also be identical.

That is not always true.

A footprint generally refers to the mounting pattern and interface geometry used by an optic. However, red dot screw compatibility can still vary based on:

• Optic design
• Screw-hole design
• Mounting plate thickness
• Direct-mount slide design
• Required screw length
• Thread specification
• Screw-head dimensions

This is why you should not purchase screws based solely on labels such as RMR or RMSc.

4. RMR Screw Size: What Should You Check?

Searches for RMR screw size are common, but there is no single rule that applies to every optic and every mounting system described as RMR-compatible.

The correct screw can depend on whether the optic is:

• Mounted directly to a compatible slide
• Installed on a mounting plate
• Installed on a plate designed for a specific pistol platform

Different mounting systems can also change the required screw length.

When checking RMR screw size, verify:

1. The exact optic model
2. The exact slide or mounting plate
3. Required thread specification
4. Required screw length
5. Required head style

Never select a screw solely because the package says “RMR screws.”

5. RMSc Screw Size: What Should You Know?

The same principle applies to RMSc screw size.

An optic using an RMSc-style footprint may require a specific mounting arrangement based on the optic and slide design.

Before choosing screws, verify the complete combination:

Optic + Firearm/Slide + Mounting Method

This is especially important with compact pistol optics, where small differences in mounting depth and dimensions can affect the correct screw length.

If you are changing from one optic to another, do not automatically reuse the previous screws without checking compatibility.

6. Replacement Red Dot Screws: What to Do When Original Screws Are Lost

Lost screws are a common reason people search for replacement red dot screws.

Before ordering replacements, gather as much information as possible.

Check the Original Product Information

The best starting point is the installation documentation for your:

• Red dot sight
• Firearm or slide
• Mounting plate

Look for the specified:

• Thread size
• Length
• Head style
• Installation instructions

Don't Guess From Appearance

Two screws can look almost identical while having different thread pitch or length.

Using an incorrect screw may damage the threads or fail to secure the optic correctly.

Build a More Flexible Screw Selection

If you work with multiple optics or frequently change mounting configurations, a multi-size red dot mounting hardware kit can be useful.

For example, the VOTATU Red Dot Mounting Screws Kit – 112 Pcs (28 Sets) includes multiple common screw types, including M3, M3.5, M4, #6-32, #4-40, #6-40, and #6-48, giving users a broader selection for gunsmithing and optics mounting applications.

VOTATU Red Dot Mounting Screws Kit – 112 Pcs (28 Sets)

A multi-size kit can help when the correct screw is known but the original hardware is missing. However, every screw should still be verified against the manufacturer's requirements before installation.

7. Pistol Red Dot Screws: Why Handgun Setups Need Extra Attention

Pistol red dot screws often involve tight tolerances and limited mounting depth.

Depending on the setup, the mounting configuration may include:

• Direct-milled slide
• Optic-ready slide
• Adapter plate
• Factory optics plate
• Aftermarket mounting plate

Adding or removing a plate can change the required screw length.

That means a screw that worked correctly for:

Optic A + Plate A

may not work for:

Optic B + Plate B

even if the optics appear to use a similar mounting pattern.

When Selecting Pistol Red Dot Screws, Check:

• Exact pistol model
• Slide cut
• Optic footprint
• Mounting plate
• Thread size
• Thread pitch
• Screw length
• Head style
• Manufacturer instructions

This complete approach is much safer than searching only for a generic “pistol red dot screw.”

For users working with multiple RMR-style optics and common screw options, the VOTATU Red Dot Sight Mounting Screws Set – 18 Sets includes options such as #6-32, #4-40, #6-40, M3, M3.5, and M4, with multiple screws in each set for DIY pistol optics mounting applications.

VOTATU Red Dot Sight Mounting Screws Set – 18 Sets

8. Mounting Problems: Common Red Dot Screw Mistakes

Choosing the correct screws is only part of successful installation.

Here are some of the most common problems.

Problem 1: The Screw Will Not Start

Possible causes include:

• Incorrect thread diameter
• Incorrect thread pitch
• Cross-threading
• Debris in the mounting hole
• Wrong screw for the mounting configuration

What to do: Stop immediately. Do not force the screw.

Start the screw carefully by hand and verify the correct specification.

Problem 2: The Screw Turns but Does Not Tighten

Possible causes can include:

• Damaged threads
• Incorrect screw length
• Incorrect screw type
• Existing mounting-hole damage

Do not continue tightening excessively in an attempt to solve the problem.

Problem 3: A Stripped Red Dot Screw

A stripped red dot screw can occur when the wrong driver bit is used, the bit is not fully seated, excessive force is applied, or the screw head becomes damaged.

To reduce the risk:

• Use the correct driver size.
• Ensure the tool is fully seated.
• Keep the tool aligned with the screw.
• Avoid excessive force.
• Follow the manufacturer's torque requirements.

If the screw head or mounting threads are already damaged, do not continue with improvised tools that may worsen the problem. Follow appropriate manufacturer or qualified professional guidance.

Problem 4: The Optic Still Moves After Installation

Possible causes include:

• Incorrect screws
• Screws that are too long and bottomed out
• Screws that are too short
• Incorrect mounting hardware
• Improper installation
• Damaged threads

First, inspect the mounting configuration and confirm that the hardware exactly matches the manufacturer's requirements.

9. How to Avoid Choosing the Wrong Red Dot Mounting Hardware

Use this checklist before installation.

Step 1: Identify the Exact Optic

Do not rely only on the footprint name.

Record the exact model.

Step 2: Identify the Mounting Method

Is it:

• Direct mount?
• Factory optic cut?
• Adapter plate?
• Aftermarket mounting plate?

Step 3: Confirm the Thread

Check the required thread diameter and pitch.

Step 4: Confirm the Screw Length

Measure or verify the required length for the complete mounting stack.

Step 5: Check the Screw Head

The head must sit correctly in the optic or plate.

Step 6: Follow Installation Specifications

Use the manufacturer's specified hardware and installation requirements.

This process significantly reduces the chance of choosing incorrect red dot mounting screws.

10. Building a Complete Red Dot Mounting Setup

Screws are only one part of the complete mounting system.

Your setup may also include:

• Red dot optic
• Mounting plate
• Adapter
• Mounting screws
• Driver tools
• Manufacturer-specified installation materials

When choosing an optic, it is useful to understand the entire mounting ecosystem before installation.

You can explore VOTATU's broader optic selection here:

VOTATU Optics Collection

When comparing optics, remember that a red dot footprint and the complete screw specification are related but not identical pieces of the compatibility process.

Screw Size vs Screw Length vs Compatibility: Quick Comparison

Frequently Asked Questions

Do all red dot sights use the same screws?

No. Red dot screws can vary by thread size, pitch, length, head style, optic, mounting plate, and slide design.

How do I find the right red dot screw size?

Start with the exact optic and mounting system manufacturer's specifications. Verify both the thread designation and the required length.

Can I use any screw that fits the hole?

No. A screw may appear to fit but still have the wrong pitch, length, or head style.

Never force a screw.

What happens if red dot screws are too long?

Red dot screws too long may bottom out before properly clamping the optic or may be incompatible with the available mounting depth. Always use the length specified for your exact mounting configuration.

What happens if red dot screws are too short?

Red dot screws too short may not provide the intended thread engagement for the mounting system. Verify the manufacturer's required screw length.

Does the RMR footprint always use the same screw size?

No. When checking RMR screw size, consider the complete optic, slide, and mounting plate combination rather than assuming all RMR-style configurations use identical screws.

Does the RMSc footprint always use the same screws?

No. RMSc screw size requirements can depend on the exact optic and mounting system.

What should I do with a stripped red dot screw?

Stop before causing additional damage. Confirm you are using the correct driver and follow appropriate manufacturer or qualified professional guidance for damaged mounting hardware.

Final Verdict: Choose Screws Based on the Complete Mounting System

The right red dot mounting screws are not chosen by appearance alone.

The correct selection requires you to consider:

Exact Optic → Red Dot Footprint → Mounting Method → Thread Size → Thread Pitch → Screw Length → Screw Head → Manufacturer Specifications

If you remember one thing from this guide, make it this:

The correct thread with the wrong length is still the wrong screw.

A reliable red dot installation requires the complete mounting system to work together. Before installing replacement red dot screws, verify the exact compatibility of the optic, slide, mounting plate, and hardware.

Whether you are searching for the right red dot screw size, replacing lost hardware, troubleshooting red dot screws too long or red dot screws too short, or dealing with a mounting problem, avoid guessing and never force incompatible threads.

For users who need multiple common sizes for different optics and mounting applications, a dedicated screw kit can make organization and hardware selection easier—but the final screw choice should always be based on the exact requirements of your individual mounting system.