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Scope / rail mount base screws (small metric) screw size

M3 · 10 mm long

Our records put Scope / rail mount base screws (small metric) on M3 screws, 10 mm long.

It is listed for M3 metric option for the same rail-mount screw range.

This entry is marked confirmed and comes from ant-supplies.uk.

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.

Scope / rail mount base screws (small metric) screw specifications

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

ThreadLengthPitchHeadDriveWhere it goesStatus
M310 mm0.5 mmnot statednot statedM3 metric option for the same rail-mount screw rangeConfirmed

Fitment records and sources

M310mmconfirmed

M3 metric option for the same rail-mount screw range

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

How to check the screw before you buy

  1. Where the manufacturer publishes a torque value, use a torque driver rather than feel.
  2. 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.
  3. 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.
  4. Length: measure from under the head to the tip for pan, button, wafer and cap heads; countersunk (flat) heads are measured overall.
  5. The record states 10 mm. Going longer risks bottoming out or touching parts behind the hole; going shorter loses thread engagement.
  6. 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.
  7. Tightening: no device-specific torque is published in these records. The site's general figure for M3 is about 80-130 N·cm into metal threads and 35-60 N·cm into plastic bosses; snug it up and stop.

Common mix-ups with M3

  • 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.
  • Eurorack is a strong known case with two competing metric standards (M2.5 for Vector rails, M3 for Schroff/DIN-style and 3U threaded rails); mixing rail types requires matching screw/nut thread.

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 Scope / rail mount base screws (small metric), closest length match first.

Questions about Scope / rail mount base screws (small metric) screws

What size screw does Scope / rail mount base screws (small metric) use?
M3 × 10 mm for M3 metric option for the same rail-mount screw range.
How long are the screws in Scope / rail mount base screws (small metric)?
The record gives 10 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 Scope / rail mount base screws (small metric)?
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 Scope / rail mount base screws (small metric)?
TechSpareWarehouse (our own store) lists M3 x 10mm, which matches the length in the records above.