Original Prusa MK4 kit screw size
M3 / M5 · length not stated in the sources
If you are replacing a screw on Original Prusa MK4 kit, the thread is M3 and M5. 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 frame and X-carriage fasteners (2.5 mm hex driver) (M3) and frame corner and rod fasteners (3 mm hex driver) (M5).
2 of the 2 records are marked confirmed, drawn from 1 source (help.prusa3d.com).
M3 means a 3 mm nominal diameter with a 0.5 mm thread pitch. Imperial look-alike: #5-40 (3.18 mm) or #4-40 — neither interchanges with M3.
Original Prusa MK4 kit 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 | Frame and X-carriage fasteners (2.5 mm hex driver) | Confirmed |
| M5 | not stated | 0.8 mm | not stated | not stated | Frame corner and rod fasteners (3 mm hex driver) | Confirmed |
Fitment records and sources
Frame and X-carriage fasteners (2.5 mm hex driver)
pitch 0.5 mm · tap 2.5 mm · clearance 3.4 mm · PH1 / Torx T10
Frame corner and rod fasteners (3 mm hex driver)
pitch 0.8 mm · tap 4.2 mm · clearance 5.5 mm · PH2 / Torx T25
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 M3 screw measures about 3 mm with calipers (usually a hair under). This device also uses M5, 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 / M5
- 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.
- Thorlabs' 16mm cage system standard plates use dual 4-40 (UNC) and M3 taps on the same plate (e.g., SP01), so metric and imperial fasteners are both valid depending on the region/kit purchased.
- Rosemount and similar field instruments quote hex driver sizes in inches (e.g. 5/64 in) rather than a metric thread.
- Espresso/coffee-equipment M5 and M6 socket-head screws (DIN 7984/UNI 9327) are cross-brand standard fasteners shared across CMA, Astoria, and La Cimbali brewing-group hardware, so a single screw often services multiple manufacturers' machines.
More in 3D Printing, CNC & Robotics
The same screw also fits
Devices whose records share a thread with Original Prusa MK4 kit, closest length match first.
- Slice Engineering Mosquito hotend also M3
- FDM hotend and extruder mounts (general) also M3
- Voron Trident also M3
- Prusa frame-to-extrusion joints also M5
- RatRig V-Core 3.1 (200x200) also M3
- NEMA 23 stepper motor face also M5
- OpenBuilds C-Beam Machine also M5
- MASSO CNC homing sensor also M3
Questions about Original Prusa MK4 kit screws
- What size screw does Original Prusa MK4 kit use?
- M3 for frame and X-carriage fasteners (2.5 mm hex driver); M5 for frame corner and rod fasteners (3 mm hex driver).
- How long are the screws in Original Prusa MK4 kit?
- 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 Original Prusa MK4 kit?
- 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.