1.25" eyepiece/diagonal/SCT visual back thumb screw screw size
M3 · length not stated in the sources
If you are replacing a screw on 1.25" eyepiece/diagonal/SCT visual back thumb screw, the thread is M3. None of the sources we found gives an exact length, so measure the original before you order.
The record covers replacement M3-0.5mm thread pitch set/thumb screws explicitly sold for 1.25" diagonal eyepiece and SCT visual back thumbscrews, and some finder/guide scope shoes.
Head and drive, as the source states them: thumb screw (knurled) head.
This entry is marked confirmed and comes from milehighastro.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.
1.25" eyepiece/diagonal/SCT visual back thumb screw 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 | Thumb screw (knurled) | not stated | Replacement M3-0.5mm thread pitch set/thumb screws explicitly sold for 1.25" diagonal eyepiece and SCT visual back thumbscrews, and some finder/guide scope shoes | Confirmed |
Fitment records and sources
Replacement M3-0.5mm thread pitch set/thumb screws explicitly sold for 1.25" diagonal eyepiece and SCT visual back thumbscrews, and some finder/guide scope shoes
pitch 0.5 mm · tap 2.5 mm · clearance 3.4 mm · PH1 / Torx T10
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 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: for thumb screw (knurled) screws, measure from under the head to the tip (countersunk heads are the exception: they 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
- 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.
- 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.
More in Cameras & Optics
The same screw also fits
Devices whose records share a thread with 1.25" eyepiece/diagonal/SCT visual back thumb screw, closest length match first.
- SmallRig camera cages and rigs also M3
- SIG SAUER ROMEO-RS reflex sight, mounting to SIG P365 pistol optic cut also M3
- Wimberley P-20 Arca-Swiss style tripod lens plate also M3
- Microscope objective turret and stage also M3
- TS-Optics Losmandy-style dovetail plate, 200mm length (L-UP7) also M3
- Wimberley AP-553 lens foot plate also M3
- Olympus BH-2 microscope frame also M3
- Aimpoint Micro T-1/T-2/H-1/H-2 standard mount screw also M3
Questions about 1.25" eyepiece/diagonal/SCT visual back thumb screw screws
- What size screw does 1.25" eyepiece/diagonal/SCT visual back thumb screw use?
- M3 for replacement M3-0.5mm thread pitch set/thumb screws explicitly sold for 1.25" diagonal eyepiece and SCT visual back thumbscrews, and some finder/guide scope shoes.
- How long are the screws in 1.25" eyepiece/diagonal/SCT visual back thumb screw?
- 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 1.25" eyepiece/diagonal/SCT visual back thumb screw?
- 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.