What is the thread pitch of an M3 screw?

0.5 mm (coarse), which is the standard pitch for M3 machine screws; a 0.35 mm fine pitch exists but is uncommon. The tap drill is 2.5 mm and the normal clearance hole is 3.4 mm.

Can I use an imperial screw instead of M3?

No. Imperial look-alike: #5-40 (3.18 mm) or #4-40 — neither interchanges with M3. Use a true M3 screw so it does not cross-thread or strip the hole.

Universal Red Dot Pattern Mounting Plate (fits Vortex Viper, Burris Fast Fire 3, UTG Reflex Micro Dot, TruGlo Tru-Tec, Crimson Trace CTS-1250, Springfield Dragonfly) screw size

M3 · 8 mm long

Universal Red Dot Pattern Mounting Plate (fits Vortex Viper, Burris Fast Fire 3, UTG Reflex Micro Dot, TruGlo Tru-Tec, Crimson Trace CTS-1250, Springfield Dragonfly) takes M3 metric screws, 8 mm long.

It is listed for manufacturer mounting instructions explicitly specify M3 x 8mm screws (torque 12 in-lb) for these optic footprints, which are also used on some archery bow-sight red-dot mounts sharing the same footprint.

This entry is marked confirmed and comes from 4shooters.com.

An M3 screw is 3 mm in diameter with a 0.5 mm pitch, tapped with a 2.5 mm drill; imperial look-alike: #5-40 (3.18 mm) or #4-40 — neither interchanges with M3.

Universal Red Dot Pattern Mounting Plate (fits Vortex Viper, Burris Fast Fire 3, UTG Reflex Micro Dot, TruGlo Tru-Tec, Crimson Trace CTS-1250, Springfield Dragonfly) screw specifications

One row per fitment record. Head, drive and torque are shown only where the source states them; pitch is the ISO coarse pitch for the thread.

Thread	Length	Pitch	Head	Drive	Torque	Where it goes	Status
M3	8 mm	0.5 mm	not stated	not stated	12 in-lb	Manufacturer mounting instructions explicitly specify M3 x 8mm screws (torque 12 in-lb) for these optic footprints, which are also used on some archery bow-sight red-dot mounts sharing the same footprint	Confirmed

Fitment records and sources

M38mmconfirmed

Manufacturer mounting instructions explicitly specify M3 x 8mm screws (torque 12 in-lb) for these optic footprints, which are also used on some archery bow-sight red-dot mounts sharing the same footprint

pitch 0.5 mm · tap 2.5 mm · clearance 3.4 mm · PH1 / Torx T10

Source

How to check the screw before you buy

Do not confuse metric mounting screws with the 1/4-20 or 3/8-16 tripod threads that cameras and clamps also carry.
Diameter: across the threads an M3 screw measures about 3 mm with calipers (usually a hair under). If yours measures noticeably more or less, it is a different thread.
Pitch: 0.5 mm from one thread crest to the next (20 crests per centimetre). A thread pitch gauge or the pitch-gauge tool settles it in seconds.
Length: measure from under the head to the tip for pan, button, wafer and cap heads; countersunk (flat) heads are measured overall.
The record states 8 mm. Going longer risks bottoming out or touching parts behind the hole; going shorter loses thread engagement.
Driver: the source does not name the drive. Standard M3 heads take PH1 for Phillips and T10 for Torx, and a 2.5 mm hex key for socket heads; a bit that fits loosely will cam out and strip the head.

Common mix-ups with M3

Eurorack rail thread varies by manufacturer: some tapped M2.5, some M3 — not a single universal standard.
Terminal-block clamp screws have manufacturer-specific torque values — over-tightening cracks the block or crushes the wire.

Pitch gauge · Screw size finder · Torque guide

Buy these screws at TechSpare Warehouse

In stock and shipped from South Carolina. Our black screws are Phillips wafer head (low profile); match the head style and length to the original before you order.

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The same screw also fits

Devices whose records share a thread with Universal Red Dot Pattern Mounting Plate (fits Vortex Viper, Burris Fast Fire 3, UTG Reflex Micro Dot, TruGlo Tru-Tec, Crimson Trace CTS-1250, Springfield Dragonfly), closest length match first.

Airsoft red dot sight mounting screw set (Laylax/Quintes Sence) also M3 × 8 mm
Wooden Camera 153200 SSD Guard (RED SCARLET) also M3 × 8 mm
Meade LX200 Barlow / eyepiece retaining screw also M3 × 8 mm
Celestron collimation screws, C5/C6/C8 SCT optical tubes also M3 × 8 mm
Gimbal / quick-release plate clamp also M3 × 8 mm
Telescope metric thumb screw for telescope parts also M3 × 8 mm
Celestron C8 Schmidt-Cassegrain OTA secondary mirror collimation screws also M3 × 8 mm
Camera cage shells (SmallRig-style) also M3 × 8 mm

Questions about Universal Red Dot Pattern Mounting Plate (fits Vortex Viper, Burris Fast Fire 3, UTG Reflex Micro Dot, TruGlo Tru-Tec, Crimson Trace CTS-1250, Springfield Dragonfly) screws

What size screw does Universal Red Dot Pattern Mounting Plate (fits Vortex Viper, Burris Fast Fire 3, UTG Reflex Micro Dot, TruGlo Tru-Tec, Crimson Trace CTS-1250, Springfield Dragonfly) use?: M3 × 8 mm for manufacturer mounting instructions explicitly specify M3 x 8mm screws (torque 12 in-lb) for these optic footprints, which are also used on some archery bow-sight red-dot mounts sharing the same footprint.
How long are the screws in Universal Red Dot Pattern Mounting Plate (fits Vortex Viper, Burris Fast Fire 3, UTG Reflex Micro Dot, TruGlo Tru-Tec, Crimson Trace CTS-1250, Springfield Dragonfly)?: The record gives 8 mm. Measure the original from under the head (overall for a countersunk head) to confirm before ordering.
What is the thread pitch of an M3 screw?: 0.5 mm (coarse), which is the standard pitch for M3 machine screws; a 0.35 mm fine pitch exists but is uncommon. The tap drill is 2.5 mm and the normal clearance hole is 3.4 mm.
What screwdriver do I need for Universal Red Dot Pattern Mounting Plate (fits Vortex Viper, Burris Fast Fire 3, UTG Reflex Micro Dot, TruGlo Tru-Tec, Crimson Trace CTS-1250, Springfield Dragonfly)?: The sources do not name the drive. For M3, Phillips heads normally take PH1 and Torx heads T10; socket heads take a 2.5 mm hex key.
Can I use an imperial screw instead of M3?: No. Imperial look-alike: #5-40 (3.18 mm) or #4-40 — neither interchanges with M3. Use a true M3 screw so it does not cross-thread or strip the hole.
How tight should the M3 screw on Universal Red Dot Pattern Mounting Plate (fits Vortex Viper, Burris Fast Fire 3, UTG Reflex Micro Dot, TruGlo Tru-Tec, Crimson Trace CTS-1250, Springfield Dragonfly) be?: The source gives 12 in-lb for manufacturer mounting instructions explicitly specify M3 x 8mm screws (torque 12 in-lb) for these optic footprints, which are also used on some archery bow-sight red-dot mounts sharing the same footprint.
Where can I buy replacement screws for Universal Red Dot Pattern Mounting Plate (fits Vortex Viper, Burris Fast Fire 3, UTG Reflex Micro Dot, TruGlo Tru-Tec, Crimson Trace CTS-1250, Springfield Dragonfly)?: TechSpareWarehouse (our own store) lists M3 x 8mm, which matches the length in the records above.

Heads up: shipping delay