How long are the screws in Prusa i3 MK3S/MK4 printed parts and extruder?

The records range from 4 to 40 mm depending on the position, so match each screw to its own hole.

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 Prusa i3 MK3S/MK4 printed parts and extruder?

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.

Where can I buy replacement screws for Prusa i3 MK3S/MK4 printed parts and extruder?

TechSpareWarehouse (our own store) lists M3 x 4mm, M3 x 5mm and M3 x 6mm, which match lengths in the records above.

Prusa i3 MK3S/MK4 printed parts and extruder screw size

M3 · 4 to 40 mm long

Our records put Prusa i3 MK3S/MK4 printed parts and extruder on M3 screws in lengths from 4 to 40 mm.

Where it is used: M3 machine screws from M3x4 to M3x40 listed by part code in the official Prusa cheatsheet.

This entry is marked confirmed and comes from 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.

Prusa i3 MK3S/MK4 printed parts and extruder 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	4–40 mm	0.5 mm	not stated	not stated	M3 machine screws from M3x4 to M3x40 listed by part code in the official Prusa cheatsheet	Confirmed

Fitment records and sources

M34-40mmconfirmed

M3 machine screws from M3x4 to M3x40 listed by part code in the official Prusa cheatsheet

pitch 0.5 mm · tap 2.5 mm · clearance 3.4 mm · PH1 / Torx T10

Source

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 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: measure from under the head to the tip for pan, button, wafer and cap heads; countersunk (flat) heads are measured overall.
The records span 4–40 mm, which means different positions take different lengths — match each hole to its own screw.
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

Label printer parts lists write M3*6 with an asterisk; that is still a true ISO M3 x 6mm machine screw.
Power-tool gearcase and clamshell screws are usually thread-forming (marked "ST") even when the parts list gives an M-size — a normal machine screw of the same size may not hold in the plastic boss.

Pitch gauge · Screw size finder · Torque guide

Buy these screws at TechSpare Warehouse

In stock and shipped from South Carolina. Our black screws are Phillips wafer head (low profile); match the head style and length to the original before you order.

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The same screw also fits

Devices whose records share a thread with Prusa i3 MK3S/MK4 printed parts and extruder, closest length match first.

E3D V6 hotend fixing kit also M3 × 4–10 mm
Voron 2.4 / Trident printed parts also M3 × 6–30 mm
Voron 2.4 gantry and panels also M3 × 8–25 mm
RatRig V-Core 3.1 (300x300) also M3 × 12 mm
CR-10 Max heat-block cooling shroud also M3 × 8 mm
Creality Sprite Extruder Pro kit also M3 × 6 mm
Bambu Lab AMS unit also M3 × 8–16 mm
Prusa MK3S extruder also M3 × 10–40 mm

Questions about Prusa i3 MK3S/MK4 printed parts and extruder screws

What size screw does Prusa i3 MK3S/MK4 printed parts and extruder use?: M3 × 4–40 mm for M3 machine screws from M3x4 to M3x40 listed by part code in the official Prusa cheatsheet.
How long are the screws in Prusa i3 MK3S/MK4 printed parts and extruder?: The records range from 4 to 40 mm depending on the position, so match each screw to its own hole.
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 Prusa i3 MK3S/MK4 printed parts and extruder?: 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.
Where can I buy replacement screws for Prusa i3 MK3S/MK4 printed parts and extruder?: TechSpareWarehouse (our own store) lists M3 x 4mm, M3 x 5mm and M3 x 6mm, which match lengths in the records above.

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