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 OuterImpact Red Dot Adapter Plate (Vortex Viper / Burris Fast Fire pattern)?

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.

Where can I buy replacement screws for OuterImpact Red Dot Adapter Plate (Vortex Viper / Burris Fast Fire pattern)?

TechSpareWarehouse (our own store) lists M3 x 8mm, which matches the length in the records above.

OuterImpact Red Dot Adapter Plate (Vortex Viper / Burris Fast Fire pattern) screw size

M3 · 8 mm long

If you are replacing a screw on OuterImpact Red Dot Adapter Plate (Vortex Viper / Burris Fast Fire pattern), the thread is M3, 8 mm long.

The record covers mounting screws attaching red dot sight to adapter, torqued to 12 in-lbs.

This entry is marked confirmed and comes from sportshooter.de.

For reference, M3 is 3 mm across the threads at 0.5 mm pitch. The imperial size people confuse it with: #5-40 (3.18 mm) or #4-40 — neither interchanges with M3.

OuterImpact Red Dot Adapter Plate (Vortex Viper / Burris Fast Fire pattern) 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-lbs	mounting screws attaching red dot sight to adapter, torqued to 12 in-lbs	Confirmed

Fitment records and sources

M38mmconfirmed

mounting screws attaching red dot sight to adapter, torqued to 12 in-lbs

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

Source

How to check the screw before you buy

Scope and accessory mounts often publish a torque value; tighten to it in a cross pattern.
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

GoPro's own official Dive Housing user guide does not itself state a metric screw size for the housing body; only third-party accessory manufacturer (INON) manuals explicitly cite M6 screws for their add-on arms/adapters attaching to the housing.
Telescope thumbscrews are sold in a wide non-metric legacy range too (1/4-20, 8-32, 10-32 on many Meade/Celestron mounts), so metric M3/M4 fitment applies mainly to newer/international accessory ecosystems (SkyWatcher, generic 1.25" accessories) and should not be assumed universal.

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 OuterImpact Red Dot Adapter Plate (Vortex Viper / Burris Fast Fire pattern), closest length match first.

Fishing reel handle and drag knob also M3 × 8 mm
OuterImpact Micro Red Dot Adapter Plate (Swampfox pattern) also M3 × 8 mm
LED drivers & furniture electronics also M3 × 8 mm
Arcade cabinet control panel also M3 × 8 mm
Wurth Elektronik WA-SPAIE plastic spacer stud also M3 × 8 mm
HP LaserJet 9000/9040/9050 series printer also M3 × 8 mm
ResMed VPAP / S8 service hardware also M3 × 8 mm
COSEL power supply terminal block (used in industrial/pump/water-treatment control panels) also M3 × 8 mm

Questions about OuterImpact Red Dot Adapter Plate (Vortex Viper / Burris Fast Fire pattern) screws

What size screw does OuterImpact Red Dot Adapter Plate (Vortex Viper / Burris Fast Fire pattern) use?: M3 × 8 mm for mounting screws attaching red dot sight to adapter, torqued to 12 in-lbs.
How long are the screws in OuterImpact Red Dot Adapter Plate (Vortex Viper / Burris Fast Fire pattern)?: 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 OuterImpact Red Dot Adapter Plate (Vortex Viper / Burris Fast Fire pattern)?: 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 OuterImpact Red Dot Adapter Plate (Vortex Viper / Burris Fast Fire pattern) be?: The source gives 12 in-lbs for mounting screws attaching red dot sight to adapter, torqued to 12 in-lbs.
Where can I buy replacement screws for OuterImpact Red Dot Adapter Plate (Vortex Viper / Burris Fast Fire pattern)?: TechSpareWarehouse (our own store) lists M3 x 8mm, which matches the length in the records above.

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