What tolerance should a 3D printed pin and hole have?

Start with the hole about 0.25 mm bigger than the pin. For high-shrink materials go up toward 0.5 mm. Print a quick step test to find the number for your material.

Why do 3D printed pins snap off?

A pin acts like a lever, so a side push loads the corner at its base, and printed parts are weakest between layers. Fillet the base, make the pin fatter and shorter, and it holds.

How do you make a 3D printed pin go into its hole easily?

Fillet the top of the hole into a funnel and round off the tip of the pin. The two then guide each other in instead of two sharp edges trying to find each other.

Should a 3D printed pin be printed vertically?

Vertical pins are common as locating features, but they break along layer lines. If a vertical pin takes real load, use a thicker cross-section pin or force it solid with micro-feature slots.

3D PrintingTolerances & FitPin tolerances

How do you design 3D printed pins that fit and don’t snap?

You press the lid down onto its locating pins and one of them pings across the bench. Or the pin never finds the hole at all. 3D printed pin tolerance comes down to a few cheap moves: a funnel on the hole, a little clearance for shrink, and a pin that’s fatter, shorter and filleted where it meets the part.

⚡ Rule of thumb

Make the hole about 0.25 mm bigger than the pin, fillet the top of the hole, fillet the pin’s base, round its tip, and make the pin as fat and as short as the job allows.

Starting point

Clearance ≈ 0.25 mm (up to 0.5 mm for high-shrink material)

Measured

Diametral gap between pin and hole

Confidence

Process-dependent

▶ Source video — Design Unbreakable Pins with Perfect Tolerances — Slant 3Dwatch on YouTube ↗

Applies to

Process: FDM / filament
Features: Vertical locating pins and their holes, alignment features, sliding pins
Materials: Higher-shrink materials need more clearance

Why it matters

A vertical pin is a lever. Push sideways on the tip and all that force lands on the corner where the pin meets the part.

Printed plastic is weakest between layers, and that corner sits right on a layer line. So the pin bends across the corner, then splits clean along the layers.

Fit fails the other way. Model the hole the exact same size as the pin and shrink means they won’t go together, or they jam and crack the part trying. A sharp pin hunting for a sharp hole doesn’t help either.

Every fix here is geometry, not slicer settings. That matters the moment someone else prints your file.

What good looks like

The hole has a fillet (a funnel) at its mouth
The hole is a hair bigger than the pin, about 0.25 mm
The pin is as thick as the design allows
A fillet where the pin meets the body, matching the funnel on the hole
A rounded or pointed tip that finds the hole on its own
No pin longer than it needs to be

How to apply it

Fillet the top edge of the hole so the pin gets funneled in.
Size the hole about 0.25 mm bigger than the pin. Go toward 0.5 mm for high-shrink materials.
Make the pin fatter. A bigger diameter is the first and easiest strength gain.
Fillet the base of the pin so the side load spreads out instead of hitting a sharp corner.
Round off the tip so the pin self-locates.
Make the pin as short as the job allows. Shorter means less lever on the base.
Do the usual hygiene on the rest of the part: chamfer the bottom edge, round the outer corners.
If it still snaps or the fit still drifts between printers, change the pin’s cross-section (see Cross-section pins).

Test it on your setup

Model a small block with the pin and a row of holes stepping the clearance 0.15 / 0.25 / 0.35 / 0.5 mm.
Print in your real material and orientation.
Pick the smallest clearance that still assembles by hand without forcing. That’s your number for that material.
Then push the pin sideways until it fails. If it breaks at the base, the fillet’s too small or the pin’s too long.

Exceptions & tradeoffs

Mind you, short and stubby isn’t always allowed. A pin that has to reach through a thick part has to be long. Then fatten it, fillet it hard, and move to a cross or micro-feature pin that doesn’t rely on a round skin.

Short pins shine on sliding features. Slant 3D calls them out for exactly that, since a sliding load is a side load all day long.

Common mistakes

A pin that’s just a plain cylinder sticking out of the partFillet its base, round its tip, and make it thicker
Hole and pin modeled the same diameterOpen the hole about 0.25 mm and fillet its mouth
A long skinny pin because it looked right in CADAs short and as fat as the job allows
Tuning the slicer until the pins fit on your printerFix it in the model so it fits on anyone’s printer

Frequently asked questions

What tolerance should a 3D printed pin and hole have?Start with the hole about 0.25 mm bigger than the pin. For high-shrink materials go up toward 0.5 mm. Print a quick step test to find the number for your material.
Why do 3D printed pins snap off?A pin acts like a lever, so a side push loads the corner at its base, and printed parts are weakest between layers. Fillet the base, make the pin fatter and shorter, and it holds.
How do you make a 3D printed pin go into its hole easily?Fillet the top of the hole into a funnel and round off the tip of the pin. The two then guide each other in instead of two sharp edges trying to find each other.
Should a 3D printed pin be printed vertically?Vertical pins are common as locating features, but they break along layer lines. If a vertical pin takes real load, use a thicker cross-section pin or force it solid with micro-feature slots.

Slant 3DSource & visual reference

Filleted hole mouth and a ~0.25 mm clearance (up to 0.5 mm) for shrink — Design Unbreakable Pins with Perfect Tolerances ↗ at 00:46.