snapfit-scad

An OpenSCAD library for round, slotted snap-fit pins that print without supports: snapfit() makes the pin and snapfit_neg() the hole it snaps into, to cut from the mating part. Add a foot to trap a plate between foot and head, or an under chamfer for pins printed in flexible filament.

Self-connecting disc	TPU foot with an under chamfer	Two discs snapped together, cut away

Install

Clone it into your OpenSCAD library folder, or next to your project:

git clone https://github.com/CameronBrooks11/snapfit-scad.git

use <snapfit-scad/snapfit.scad>;

Set $fn in your own file. The library’s own $fn doesn’t carry through use, so without it you get OpenSCAD’s coarse default: the default pin renders in 72 triangles, against 996 at $fn = 128.

The pin and the hole

The pin is a column of diameter dia with a cone-shaped head on top. The head’s base is lip wider than the column, and a slot down through the head lets its two halves flex together as it goes through the hole.

snapfit_neg() is the matching hole, to subtract from the part the pin goes into. Its throat is dia across, the column’s own size, so the head has to squeeze through, then a pocket above gives the head neg_tol of clearance once it’s through.

thickness changes both:

• On snapfit() it adds a foot: a cone on the column, thickness below the head. The other part is trapped between foot and head.
• On snapfit_neg() the narrow hole is thickness deep, the plate the head snaps past.

Parameters

Both modules compute the head from dia and lip: it’s (dia + lip) / 2 tall, with a base radius of (dia + lip) / 2, and narrows to dia / 2 across at the top.

snapfit

Parameter	Default	Description
dia	3	Column diameter, before col_tol.
lip	0.75	How much wider the head’s base is than dia.
col_h	6	Column height, from the base to the head.
col_tol	0.1	Taken off the column’s radius.
slot_ratio	0.7	The slot’s depth, as a fraction of column plus head height.
thickness	undef	If set, adds a foot with this gap below the head.
under_chamfer_angle	undef	If set, adds a cone of this angle under the head, so the catch is a slope instead of a step. Added for printing in flexible filament; the TPU example uses 45.

snapfit_neg

Parameter	Default	Description
dia, lip, col_h, slot_ratio	as above	Match the pin.
neg_tol	0.5	Clearance around the head in the pocket.
thickness	undef	If set, the hole is this deep; otherwise col_h.
flip	false	Mirrors the hole top to bottom, for a pin entering from above.
under_chamfer_angle	undef	Clearance for a pin with an under chamfer.

Positional arguments follow the order in the tables, as in the examples: snapfit(dia, lip, col_h, col_tol, slot_ratio, thickness = thickness).

Use these names. Older copies of this README listed diameter, column_height, column_tolerance and negative_tolerance, which OpenSCAD ignores with a warning.

Examples

• examples/self_connecting_snap.scad: a 10 mm disc with a pin on top and a hole underneath, so copies stack. Seated, each copy rests on the foot of the one below, 10 mm higher.
• examples/pcb_feet_tpu.scad: a tapered foot with a short pin and an under chamfer, to push into a board’s mounting hole.
• examples/stacked_pair.scad: two self-connecting discs seated together and cut in half, to show how the pin sits in the hole. For looking at, not printing.

The earlier versions of the first two were printed on a Prusa MK3S with a 0.4 mm nozzle, with these settings from their PrusaSlicer projects (removed from the repo but in its history). The rewritten geometry hasn’t been printed yet.

	self_connecting_snap	pcb_feet_tpu
Filament	PLA (Polymaker PLA Pro), 210 °C, bed 60 °C	Generic FLEX, 228 °C (230 first layer), bed 50 °C
Layer height	0.05 mm, first layer 0.2 mm	0.1 mm, first layer 0.2 mm
Perimeters	3	4
Infill	25 % gyroid	0 %
Top / bottom layers	14 / 10	8 / 7
Other	5 mm brim	extrusion multiplier 1.12

Checks

just test takes about 1 s on OpenSCAD 2026.10.15. It checks each module’s size, with and without thickness and under_chamfer_angle, and the examples. Then it stacks two self-connecting copies (tests/fit.scad). Seated, they only touch. 0.1 mm closer, they overlap. Lifted 1 mm, the head overlaps the throat for 0.625 mm, which is the snap. It also checks that flip mirrors the hole. The checks are geometry: how well a pin snaps and holds depends on the material and the print. just images renders the pictures above.

Origin and licence

The library is a rewrite, under MIT, of an idea from jpearce’s Parametric OpenSCAD Snap Fit on Thingiverse: a slotted round pin and the hole it snaps into. The code is new; the modules and their parameters keep their names and order, so existing calls still work, though the pin’s and hole’s exact shapes have changed. The earlier GPL-3.0 versions are in this repository’s history. MIT; see LICENSE.