Bondtech primary gear (8mm bore) screw size
M4 · 3 mm long
Our records put Bondtech primary gear (8mm bore) on M4 screws, 3 mm long.
It is listed for grade 12.9 set screw.
Head and drive, as the source states them: set screw (headless) head.
This entry is marked confirmed and comes from test.bondtech.se.
M4 means a 4 mm nominal diameter with a 0.7 mm thread pitch. Imperial look-alike: #8-32 (4.17 mm) — the standard US PC/rack screw, close but not the same.
Bondtech primary gear (8mm bore) 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 | 3 mm | 0.7 mm | Set screw (headless) | not stated | grade 12.9 set screw | Confirmed |
Fitment records and sources
grade 12.9 set screw
pitch 0.7 mm · tap 3.3 mm · clearance 4.5 mm · PH2 / Torx T20
How to check the screw before you buy
- Into printed plastic, the screw either self-taps or needs a heat-set insert; machine screws straight into plastic strip easily.
- 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: for set screw (headless) screws, measure from under the head to the tip (countersunk heads are the exception: they are measured overall).
- The record states 3 mm. Going longer risks bottoming out or touching parts behind the hole; going shorter loses thread engagement.
- 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
- Grounding-lug screws on Siemens and Beckhoff gear (M4) are earth hardware, not structural mounting screws — don't reuse them to hold a module.
- M4 and 6-32 UNC share a nominal diameter with different pitch — a classic cross-thread in US-market kits.
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Devices whose records share a thread with Bondtech primary gear (8mm bore), closest length match first.
- Cognex In-Sight 9000 machine vision system also M4 × 3 mm
- Traxxas Spartan SR (Model 103076-4) boat also M4 × 3 mm
- Maytronics Dolphin Supreme M4 Robotic Pool/Pond Cleaner also M4
- InMoov open-source robot also M4
- Ultimaker Original heated bed / Z-stage upgrade kit also M4
- Inventables X-Carve 300W 24VDC spindle kit also M4
- Makeblock mBot Neo/mBot2 assembly kit also M4
- BigTreeTech Manta M8P printer mainboard also M4
Questions about Bondtech primary gear (8mm bore) screws
- What size screw does Bondtech primary gear (8mm bore) use?
- M4 × 3 mm for grade 12.9 set screw.
- How long are the screws in Bondtech primary gear (8mm bore)?
- The record gives 3 mm. Measure the original from under the head (overall for a countersunk head) to confirm before ordering.
- 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 Bondtech primary gear (8mm bore)?
- 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.