Original description by Iker Libano | KNIN Custom, copied and adjusted to the FreeCAD version (changes in Italics):

3D Printable Screw Generator for FreeCAD

This is a fully editable FreeCAD file designed to generate screws specifically optimized for 3D printing.

Most standard metric threads are designed for metal manufacturing, not for FDM printing.
That means they usually have:

• overly sharp thread profiles
• unsupported overhangs
• tiny fragile tips
• unreliable tolerances

This generator solves those problems by allowing you to fully customize the geometry of the thread depending on:

• your printer
• your material
• your layer height
• your nozzle size

The goal is simple:
Create screws that print reliably and work consistently.

Features

• Fully parametric FreeCAD file
• Adjustable thread angle
• Adjustable minimum thread section
• Adjustable tolerances
• Automatic nut generation
• Adjustable bolt head height
• Adjustable nut height
• Adjustable tip chamfer
• Adjustable nut chamfer
• Hole body
• Horizontal split screw version for extra strength
• Optimized specifically for FDM printing
• Works great with PLA and PETG

YouTube video

Full explanation and engineering breakdown here:

The video explains:

• how printable threads work
• why standard threads fail
• how to optimize screws for FDM printing
• how to use this generator
• how to create stronger printable screws

Important: How printable threads work

A standard metric thread is usually NOT ideal for 3D printing.

There are 2 major problems:

1. Overhang angle

Very sharp thread angles create unsupported geometry.
Your printer ends up printing partially in the air, which causes sagging and poor precision.

This generator allows you to adjust the thread angle so the screw prints cleanly without supports.

Recommended values:

• 35° → better mechanical performance
• 45° → maximum reliability

2. Tiny sharp thread tips

Standard threads end in extremely small sharp points.

FDM printers have a physical limit regarding the smallest detail they can print reliably.
If the tip is too thin, the thread becomes inconsistent and fragile.

The parameter SECTION_MIN controls the minimum flat section at the tip of the thread.

Recommended values:

• 0.3 mm minimum
• Higher values = easier printing and stronger threads
• Lower values = more compact threads and better mechanical advantage

User parameters

Only the non-hidden parameters should be modified.

THREAD_LENGTH

Length of the threaded section.

DIAMETER_EXT

Outer diameter of the screw.

SECTION_MIN

Minimum flat section at the tip of the thread.

ANGLE

Angle of the thread walls.

CLEARANCE

Clearance between screw and nut.

Recommended:
0.15 mm

NUT

Nut size multiplier.

• 1 = standard nut
• 2 = double-size nut
• etc.

CHAMFER_TIP

Size of the screw tip chamfer (0 mm means no chamfer)

CHAMFER_NUT

Size of the Nut Chamfer (both sides), if set to 0 the nut will not be chamfered

BOLT_HEAD_HEIGHT

Height of the bolt head (if 0 the original scaling with NUT will be used)

NUT_HEIGHT

Height of the nut (if 0 the original scaling with NUT will be used)

HOLE_HEIGHT

Height of the hole-body generated

3. Export your model

The FreeCAD file contains four parts you can export:

• Screw Vertical Print
  • Contains a screw intended to be printed in the vertical direction
• Nut
  • Contains the nut corresponding the generated screw
• Hole Body
  • Contains a body of the hole needed for the screw (can be subtracted from your other designs)
• Screw Horizontal Print
  • Contains a split screw intended to be printed in the horizontal direction with a centering piece

Notes

• This is Version 1 and will probably evolve over time.
• Some parameter combinations may generate FreeCAD errors (sometimes these errors can be resolved by making 1 μm adjustments to e.g. SECTION_MIN, this will not affect the print).
• The red labels update automatically and may take a few seconds.
• This project is designed mainly for FDM printers.

Feedback / Suggestions

If you have ideas, improvements or find bugs, feel free to leave a comment.