SO-100 / SO-ARM100 robot arm (LeRobot) screw size
M2 / M3 · length not stated in the sources
If you are replacing a screw on SO-100 / SO-ARM100 robot arm (LeRobot), the thread is M2 and M3. 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 feetech servo horn and bracket mounting (M2) and 3D-printed link and servo case assembly (M3).
2 of the 2 records are marked confirmed, drawn from 1 source (github.com/TheRobotStudio/SO-ARM100 BOM).
M2 means a 2 mm nominal diameter with a 0.4 mm thread pitch. Imperial look-alike: #2-56 UNC (2.18 mm) is close but not interchangeable.
SO-100 / SO-ARM100 robot arm (LeRobot) 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 |
|---|---|---|---|---|---|---|
| M2 | not stated | 0.4 mm | not stated | not stated | Feetech servo horn and bracket mounting | Confirmed |
| M3 | not stated | 0.5 mm | not stated | not stated | 3D-printed link and servo case assembly | Confirmed |
Fitment records and sources
Feetech servo horn and bracket mounting
pitch 0.4 mm · tap 1.6 mm · clearance 2.4 mm · PH0 / Torx T6
3D-printed link and servo case assembly
pitch 0.5 mm · tap 2.5 mm · clearance 3.4 mm · PH1 / Torx T10
How to check the screw before you buy
- Printer and CNC builds usually publish a bill of materials; when it lists a length, follow it, since extrusion T-nuts and motor faces have fixed thread depths.
- Diameter: across the threads an M2 screw measures about 2 mm with calipers (usually a hair under). This device also uses M3, so measure each screw rather than assuming they match.
- Pitch: 0.4 mm from one thread crest to the next (25 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 M2 heads take PH0 for Phillips and T6 for Torx, and a 1.5 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 M2 is about 25-40 N·cm into metal threads and 12-20 N·cm into plastic bosses; snug it up and stop.
Common mix-ups with M2 / M3
- Most consumer gadget teardowns (robot vacuums, toothbrushes, e-readers, VR headsets) list only the driver bit, not the thread — measure before ordering.
- M2 (2.00mm, 0.4mm pitch) is NOT the same as #2-56 UNC (2.18mm) — close enough to cross-thread and strip if forced.
- Pond/aquarium equipment manuals aimed at consumers rarely specify exact thread pitch or length for internal fasteners, since these are considered non-user-serviceable; distributor-level assembly/service manuals (e.g., Maytronics internal documents) are a better source than end-user guides.
- M3 (3.0mm, 0.5mm pitch) is not #6-32 UNC (~3.5mm) — they look identical and cross-thread, the single most common PC-building mistake.
More in 3D Printing, CNC & Robotics
The same screw also fits
Devices whose records share a thread with SO-100 / SO-ARM100 robot arm (LeRobot), closest length match first.
- SIBOOR Voron 2.4 350 / Voron 0.2 R1 kits also M3
- Voron Afterburner toolhead also M3
- MGN9 linear rail also M3
- 2020 extrusion T-nuts (light duty) also M3
- MGN12 linear rail also M3
- NEMA 17 stepper motor face also M3
- OpenBuilds gantry plate brackets also M3
- VEX / Actobotics channel and gussets also M3
Questions about SO-100 / SO-ARM100 robot arm (LeRobot) screws
- What size screw does SO-100 / SO-ARM100 robot arm (LeRobot) use?
- M2 for feetech servo horn and bracket mounting; M3 for 3D-printed link and servo case assembly.
- How long are the screws in SO-100 / SO-ARM100 robot arm (LeRobot)?
- 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 M2 screw?
- 0.4 mm (coarse), which is the standard pitch for M2 machine screws; a 0.25 mm fine pitch exists but is uncommon. The tap drill is 1.6 mm and the normal clearance hole is 2.4 mm.
- What screwdriver do I need for SO-100 / SO-ARM100 robot arm (LeRobot)?
- The sources do not name the drive. For M2, Phillips heads normally take PH0 and Torx heads T6; socket heads take a 1.5 mm hex key.
- Can I use an imperial screw instead of M2?
- No. Imperial look-alike: #2-56 UNC (2.18 mm) is close but not interchangeable. Use a true M2 screw so it does not cross-thread or strip the hole.