Functional parts · 2026
3D printing tolerances: clearances, holes and threads
How much clearance does a 3D printed part need to fit?
On a well-tuned FDM printer, a small part comes out 0.1–0.3 mm off the design; in resin, 0.05–0.15 mm. So wherever something has to fit, you leave clearance: in FDM, up to 0.1 mm per side for a press fit, 0.2–0.3 mm for a sliding fit and 0.4–0.5 mm for something that turns freely. Holes print slightly undersized, and printed threads work from M6 upwards; below that, brass inserts. Fabrishare is a network of makers: post your project for free and get quotes within 24–48 hours.
FDM and resin tolerances: how far off is a printed part?
Reference values, not a data sheet: they change with the printer, the material and how the part is oriented.
| Technology | Typical deviation | What makes it worse |
|---|---|---|
| FDM, small part (up to about 5 cm) | 0.1–0.3 mm on a well-tuned printer; some manufacturers' guides allow up to ±0.5 mm | Small holes and fillets, the first layer (slightly squashed) and overhangs |
| FDM, large part | Grows with size: around 0.5% of the dimension | Shrinkage as it cools, especially ABS and ASA, and long flat parts that warp |
| Resin | 0.05–0.15 mm | Long, thin parts, which can bend as they cure, and faces that carried supports |
Deviation differs on each axis: height depends on the layer height, and width and depth on the nozzle and the maker's calibration. If a dimension is critical, say so in the project: the maker will orient the part so that dimension comes out best.
Tolerances and clearances: how much gap between two parts?
Clearance per side, meaning on each wall: an 8 mm shaft with 0.2 mm per side needs an 8.4 mm hole in the design. These are starting points; for tight fits, a test print is the safer route.
| Fit | What for | FDM (per side) | Resin (per side) |
|---|---|---|---|
| Press fit | A pin, a magnet or a bearing that stays put without glue | 0–0.1 mm | 0–0.05 mm |
| Sliding fit | A lid that goes on and off, a drawer, a part assembled by hand | 0.2–0.3 mm | 0.05–0.1 mm |
| Loose (running) fit | A turning shaft, a hinge, print-in-place moving parts | 0.4–0.5 mm | 0.15–0.2 mm |
Why do holes print undersized, and why do parts shrink?
Holes
In FDM, small holes come out narrower than designed: in one PLA test, by about 0.1 mm in diameter, while pins came out slightly fatter. A horizontal hole also sags a little at the top. There are two fixes: draw it slightly bigger, or print it tight and finish it with a drill bit of the exact size, which is the most accurate option for a shaft or a bearing.
Plastic shrinkage
ABS and ASA shrink as they cool, by roughly 0.5 to 1.5%: on a 100 mm part, between half a millimetre and a millimetre and a half. The maker compensates by scaling the part in the slicer. PLA and PETG shrink far less.
Resin
Resin contracts slightly as it cures, and long, thin parts can bend. Each printer's profiles already compensate for much of it. Standard resin is stiff and brittle: for clips, snap fits and parts that flex, there are tough and flexible resins.
Printed thread, brass insert or nut?
Five ways to put a screw into a printed part, from the quickest to the strongest:
| Option | When | Watch out for |
|---|---|---|
| Printed thread | Large threads, caps and lids screwed on by hand; in FDM, from M6 up | Below M5–M6 it prints badly in FDM; leave 0.1–0.2 mm per side and print with the axis vertical |
| Thread-forming screw for plastics | Parts assembled once or rarely opened | Needs a pilot hole of the right size; the thread strips if opened often |
| Tapping the hole | Printed hole, then threaded by hand with a tap; works in resin too | Survives few assemblies, like a thread-forming screw |
| Brass threaded insert | Enclosures and parts opened many times (M2 to M8) | Pressed in with heat, at the plastic's printing temperature plus about 10 °C; ask for it, as not every maker fits them |
| Captive nut | The strongest, cheapest joint: a standard nut in a hexagonal pocket | The pocket needs clearance and room in the design; sometimes the print is paused to drop it in |
Of the 110 registered requests between May and October 2026, 26 were for spare and functional parts and 5 for prototypes and technical parts; among them, a housing with an M48 thread, the kind of size where a printed thread works well.
What to tell the maker so it fits first time
With a file, the maker prints what is drawn. If the clearances aren't in the design, or you're not sure they are, these details save a second version:
- The critical dimensions: which ones must be exact and which don't matter. A sketch or a PDF with them marked is enough.
- The fit you want at each joint: press, sliding or turning.
- The part it fits with: real measurements taken with callipers or, better, the size of the screw, bearing or shaft.
- The material and where it will work: heat, sun, load, moisture.
- The file, ideally STEP rather than STL: it keeps exact dimensions and the maker can adjust a hole without redrawing the part.
Why order a test fit before the run?
- 1
A test part
Just the area that fits, or the whole part if it's small: a small FDM part costs about €10, excluding VAT and shipping.
- 2
Check it
Against the real thing: the screw, the shaft, the lid. Note what's tight and what's loose.
- 3
Correct it
The maker adjusts the clearances in the model, or you do in your design. With a STEP file it's quick.
- 4
The real part or the run
Once the fit is approved, in the final material. For reference, 100 identical small FDM parts come to about €3.65 each.
Guides for parts that have to fit
Gears
Which material resists wear, the module and the backlash between teeth.
3D printed gears and mechanical partsEnclosures
Clearance for the board, bosses for inserts and ventilation.
Custom electronics enclosuresAdapters
Joining two things that don't fit: pipes, dust extraction, mounts.
Custom adaptersPrototypes
From the first version to the one that fits, before paying for a mould.
Rapid prototyping with 3D printingSpare parts
Which spare parts can be printed and how to measure the broken one.
3D printed spare partsOutdoors and heat
Materials that stand up to sun, water and temperature without deforming.
Parts for outdoor use
How to order a part that has to fit
- 1Post your project for free with the file, the critical dimensions, the fit you want and what it has to fit with.
- 2Makers in the network send you their offer with price, material and lead time within 24–48 hours.
- 3You compare, choose, and the maker prints it and ships it to you.
Frequently asked questions
What tolerance can a 3D printer hold?
In FDM, a small part is 0.1–0.3 mm off on a well-tuned printer, and some manufacturers' guides allow up to ±0.5 mm; on large parts the deviation grows, to around 0.5% of the dimension. In resin, 0.05–0.15 mm.
How much clearance should I leave between two printed parts?
In FDM, per side: up to 0.1 mm for a press fit, 0.2–0.3 mm for a sliding fit and 0.4–0.5 mm for something that turns freely. In resin, much less: 0 to 0.2 mm. These are starting points; for tight fits, order a test print first.
Why do 3D printed holes come out too small?
Because of the way the printer traces circles: in one PLA test, holes came out about 0.1 mm narrower in diameter. Draw them slightly bigger, or print them tight and finish them with a drill bit of the exact size, which is the most accurate option for shafts and bearings.
Can threads be 3D printed?
Yes, large ones: in FDM, from M6 up, with 0.1–0.2 mm clearance per side and ideally with the axis vertical. Below M5–M6 they print badly. For small screws, use brass threaded inserts, a captive nut or tap the hole.
What is a heat-set brass insert?
A brass part threaded on the inside that is pressed into a hole in the printed part with heat, at the plastic's printing temperature plus about 10 °C. They come from M2 to M8 and survive many assemblies. Not every maker fits them: ask for them in the project.
Does a part shrink when it's printed?
ABS and ASA do, by roughly 0.5 to 1.5% as they cool: half a millimetre to a millimetre and a half over 100 mm. The maker compensates by scaling the part. PLA and PETG shrink far less, and resin contracts slightly as it cures.
Resin or FDM for parts that have to fit?
Resin for small, precise parts under little load: it's off by 0.05–0.15 mm. FDM for functional parts that take load, in PETG, ASA or nylon, with more clearance. If in doubt, say in the project what the part does and the maker will suggest the technology.
How much does a test fit cost?
A small FDM part costs about €10 (€6–€17), excluding VAT and shipping. If the part is large, just the area that fits can be printed. Each maker gives the exact price in their offer.
Which file should I send for a part with exact dimensions?
STEP rather than STL: it keeps exact dimensions and the maker can adjust a hole or a clearance without redrawing the part. Add a sketch or a PDF with the critical dimensions and the fit you want. An STL prints without any problem too.