Thorlabs ELL21/M rotation mount screw size
M4 · length not stated in the sources
If you are replacing a screw on Thorlabs ELL21/M rotation mount, the thread is M4. None of the sources we found gives an exact length, so measure the original before you order.
It is listed for product spec states M4 x 0.7 tap for post mounting.
This entry is marked confirmed and comes from thorlabs.com.
An M4 screw is 4 mm in diameter with a 0.7 mm pitch, tapped with a 3.3 mm drill; imperial look-alike: #8-32 (4.17 mm) — the standard US PC/rack screw, close but not the same.
Thorlabs ELL21/M rotation mount 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 |
|---|---|---|---|---|---|---|
| M4 | not stated | 0.7 mm | not stated | not stated | Product spec states M4 x 0.7 tap for post mounting | Confirmed |
Fitment records and sources
Product spec states M4 x 0.7 tap for post mounting
pitch 0.7 mm · tap 3.3 mm · clearance 4.5 mm · PH2 / Torx T20
How to check the screw before you buy
- Camera and optics hardware often uses short screws into thin threaded plates, so check engagement before tightening fully.
- Diameter: across the threads an M4 screw measures about 4 mm with calipers (usually a hair under). If yours measures noticeably more or less, it is a different thread.
- Pitch: 0.7 mm from one thread crest to the next (14.29 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 M4 heads take PH2 for Phillips and T20 for Torx, and a 3 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 M4 is about 2.0-3.0 N·m into metal threads and 0.8-1.4 N·m into plastic bosses; snug it up and stop.
Common mix-ups with M4
- OEM laundry-parts storefronts (Alliance Laundry) are a very reliable source because they name the exact DIN standard and thread callout in the product title itself, unlike most service manuals which just show an exploded-view drawing.
- Camera rig/cage accessories (SmallRig, Wooden Camera/Metabones) frequently mix M4 structural screws with 1/4-20 and 3/8-16 imperial mounting points on the same product — verify which specific fastener a manual is referencing before ordering replacements.
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Browse all 278 in Cameras & Optics →The same screw also fits
Devices whose records share a thread with Thorlabs ELL21/M rotation mount, closest length match first.
- Celestron NexStar 8 eyepiece holder also M4
- Optic/scope ring mounting screw manufactured to engineering drawing (fastener supplier drawing, generic optics mount hardware) also M4
- OpenFlexure Delta Stage frame also M4
- Vivotek IT9360-H / IT9380-H dome camera also M4
- i-PRO / Panasonic WV-QWL100 camera mount bracket also M4
- Newport M-SP-2 optical post also M4
- Gimbal stabilizer arm clamp also M4
- Edmund Optics metric post kit also M4
Questions about Thorlabs ELL21/M rotation mount screws
- What size screw does Thorlabs ELL21/M rotation mount use?
- M4 for product spec states M4 x 0.7 tap for post mounting.
- How long are the screws in Thorlabs ELL21/M rotation mount?
- 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 M4 screw?
- 0.7 mm (coarse), which is the standard pitch for M4 machine screws; a 0.5 mm fine pitch exists but is uncommon. The tap drill is 3.3 mm and the normal clearance hole is 4.5 mm.
- What screwdriver do I need for Thorlabs ELL21/M rotation mount?
- The sources do not name the drive. For M4, Phillips heads normally take PH2 and Torx heads T20; socket heads take a 3 mm hex key.
- Can I use an imperial screw instead of M4?
- No. Imperial look-alike: #8-32 (4.17 mm) — the standard US PC/rack screw, close but not the same. Use a true M4 screw so it does not cross-thread or strip the hole.