Thorlabs Fixed Mirror Mounts (post-mountable) screw size
M3 / M4 · length not stated in the sources
Our records put Thorlabs Fixed Mirror Mounts (post-mountable) on M3 and M4 screws. None of the sources we found gives an exact length, so measure the original before you order.
There are 2 separate fitment records for it, including post mounting tapped hole option (4-40 or M3) (M3) and post mounting tapped hole option (8-32 or M4) (M4).
2 of the 2 records are marked confirmed, drawn from 1 source (thorlabs.com).
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.
Thorlabs Fixed Mirror Mounts (post-mountable) 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.
| Thread | Length | Pitch | Head | Drive | Where it goes | Status |
|---|---|---|---|---|---|---|
| M3 | not stated | 0.5 mm | not stated | not stated | post mounting tapped hole option (4-40 or M3) | Confirmed |
| M4 | not stated | 0.7 mm | not stated | not stated | post mounting tapped hole option (8-32 or M4) | Confirmed |
Fitment records and sources
post mounting tapped hole option (4-40 or M3)
pitch 0.5 mm · tap 2.5 mm · clearance 3.4 mm · PH1 / Torx T10
post mounting tapped hole option (8-32 or M4)
pitch 0.7 mm · tap 3.3 mm · clearance 4.5 mm · PH2 / Torx T20
How to check the screw before you buy
- Keep material and finish the same as the original (often stainless) on equipment that is cleaned or sterilised.
- Diameter: across the threads an M3 screw measures about 3 mm with calipers (usually a hair under). This device also uses M4, so measure each screw rather than assuming they match.
- 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.
- 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.
- 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 / M4
- 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 rail thread varies by manufacturer: some tapped M2.5, some M3 — not a single universal standard.
- Display mounts mix systems: the screen side is metric M4/M6, but the wall side of many mounts uses imperial wood screws such as #14 x 2.5in.
- Dashcam mounts advertised as '1/4" M4 screw joint' have two different threads: the 1/4"-20 camera thread and a separate M4 grub screw for the ball joint — don't order the wrong one.
More in Medical & Laboratory
The same screw also fits
Devices whose records share a thread with Thorlabs Fixed Mirror Mounts (post-mountable), closest length match first.
- Blind-tapped DN16CF ConFlat vacuum flange (metric) also M4
- Medfusion 3500 syringe infusion pump also M4
- Thorlabs 100mm compact motorized translation stage also M4
- TSC TA200/TA300 barcode printer also M3
- Agilent 1100 LC/MSD mass spectrometer also M3
- Fresenius Medical Care 2008 Series hemodialysis machine also M3
- Waters Xevo / Acquity instrument panel screw also M4
- Ottobock 17AD1 multifunctional ankle joint screw also M4
Questions about Thorlabs Fixed Mirror Mounts (post-mountable) screws
- What size screw does Thorlabs Fixed Mirror Mounts (post-mountable) use?
- M3 for post mounting tapped hole option (4-40 or M3); M4 for post mounting tapped hole option (8-32 or M4).
- How long are the screws in Thorlabs Fixed Mirror Mounts (post-mountable)?
- None of the sources states a length. Remove one screw and measure it from under the head to the tip (overall for a countersunk head).
- 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 Thorlabs Fixed Mirror Mounts (post-mountable)?
- 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.