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3DAI
Free · runs in your browser · ISO metric M3-M30

Screw Thread Generator (Bolt and Nut STL)

Pick an ISO metric size from M3 to M30, coarse or fine pitch, or type your own diameter and pitch. Choose a hex head, socket cap or threaded rod, set the length and the print tolerance, and screw the nut on in 3D. Then download a printable STL or 3MF of the bolt, nut and test block.

Loading the thread generator...

How to make a 3D printed bolt and nut

  1. 1

    Pick a size

    Choose an ISO metric size (M3-M30) and a coarse or fine pitch, or Custom to type any diameter and pitch, in mm or inches.

  2. 2

    Pick the parts

    A bolt with a hex head, a socket cap head or no head (a threaded rod), a matching hex nut, and a threaded test block to check the fit.

  3. 3

    Set the fit

    The print tolerance (0.3 mm by default) is added to the nut and the hole only, so the bolt stays true to size. Screw the nut on in the 3D preview.

  4. 4

    Download and print

    Save each part as an STL, or all of them as one STL or a 3MF. The bolt stands on its head and the nut lies flat, so neither needs supports.

The settings

SizeISO metric M3-M30 with the coarse pitch from the ISO 261/262 table, plus the standard fine pitches for M8-M30. Custom: any diameter from 2 to 60 mm and any pitch up to half the diameter.
Bolt headHex head (30° chamfer on the bed side), socket cap (cylinder head with a hex socket and a 45° roof so it prints without a bridge), or none for a threaded rod chamfered at both ends.
LengthThreaded length under the head, 2 pitches to 200 mm. The whole shank is threaded and the tip has a 45° chamfer so the first turn starts easily.
Head and nut sizeAuto by default, from approximate ISO 4014 (hex head), ISO 4762 (socket head) and ISO 4032 (nut) proportions. They are approximate, not certified dimensions; type your own to override them.
Print toleranceThe total clearance on the diameter, 0.1-0.5 mm (0.3 mm by default). The nut and the test block are enlarged by it: every flank gets half of it as a gap.
Left-handMirrors every part, so the nut turns on anticlockwise. Used for reverse threads, e.g. on a left-side axle.
Test blockA block with the same internal thread as the nut, taller, for testing the fit before printing a set.

Rules of thumb behind the warnings

The tool warns, but does not stop you, when a thread looks too small, too tight or too loose for a typical FDM printer with a 0.4 mm nozzle. These are rounded rules of thumb, not limits: a tuned printer or a resin printer can go finer.

CheckRule of thumbSource
Thread profileISO 68-1 basic profile: 60° flanks, H = 0.866 × pitch, crest flat P/8, root flat P/4, minor diameter = D − 1.0825 × P.ISO 68-1 and ISO 261/262, as summarised on Wikipedia "ISO metric screw thread"
ClearanceAbout 0.2-0.4 mm in total on the diameter for FDM; tune it with a test print.SelfCAD, "3D Printing Threads and Screws: Key Settings and Tips"
Small threadsBelow about M5-M6, printed threads come out weak and rough; use a resin printer, a metal screw or a heat-set insert.SelfCAD, same article
OrientationPrint threads standing up (axis vertical) with fine layers, so each turn is a clean round layer.SelfCAD, same article

Rules of thumb, not guarantees: every printer differs. Sites named on this page are named only to describe compatibility; The3DAI is not affiliated with or endorsed by them.

Need a custom part? Describe it and get a printable STL with AI

A bracket, a knob, a cap that screws on, a holder or a figure: type what you need and get a printable STL, or turn a photo into a 3D model. The AI generators use credits; this thread generator does not.

Describe it: text to STL →Image to STL

More free 3D printing tools

STL viewerScale STL3D print cost calculator

Thread generator FAQ

Pick the size here, keep the 0.3 mm tolerance and download the STL. Print the bolt standing on its head and the nut flat, both without supports, with 0.1-0.15 mm layers and slow outer walls. If the nut is tight, print the test block with a larger tolerance; if it wobbles, use a smaller one.
Most FDM printers need 0.2-0.4 mm in total on the diameter; 0.3 mm is the default here. The tolerance is added to the nut and the hole only, so the bolt keeps its true size and also fits a metal nut. Resin prints are usually more accurate, so try a smaller value there.
The bolt is modelled at the ISO basic size, so a well-printed M8 bolt fits a metal M8 nut of the same pitch, and a metal bolt fits the printed nut with the tolerance you set. Printers vary: if a metal nut is tight, scale the bolt down slightly in your slicer or sand it lightly.
The pitch is the distance between two threads. Coarse is the default for each size (1.25 mm for M8). Fine pitches (1 or 0.75 mm for M8) have shallower teeth and hold vibration better, but printed fine threads are less forgiving. For printing, coarse pitch is usually the better choice.
On a 0.4 mm nozzle, about M6 is the practical lower limit for strong threads; M3-M5 print but come out weak and rough. For small sizes, model a plain hole and use a heat-set insert or a metal screw, or print on a resin printer.
Tick Left-hand thread. Every part is mirrored, so the nut screws on anticlockwise. Use left-hand threads where a right-hand one would loosen as it turns, for example on a left-side pedal or axle.
It is a block with the same internal thread as the nut, but taller. Print it with your bolt to check the fit before you print a full set, or print a few with different tolerances side by side to find the best setting for your printer and filament.
No. The parts are built in your browser. Only the open-source geometry engine (manifold-3d) is downloaded once from a public CDN. No account, no credits and no watermark.