FDM Design Reference: Tolerances, Clearances and Wall Thickness

This is a reference page for designing parts to be printed with FDM. It collects the numbers people ask us for most: tolerances, hole sizes, clearances for different fits, wall thickness, threads, build size and material limits. Bookmark it and check your model against it before you upload.

Two kinds of numbers appear below. Figures for ZeroCore prints come from our own FAQ and material pages. Figures marked "typically" are general FDM starting points, not guarantees. Fits depend on geometry and material, so test anything critical before committing to a batch.

Dimensional Tolerances

Expect ±0.2–0.5 mm on a typical FDM part. Smaller features sit at the tighter end of that range; long or large parts can drift towards the looser end.

Feature	What to expect	Design tip
General dimensions	±0.2–0.5 mm	Don't rely on a fit tighter than this without testing
Holes	Come out about 0.1–0.2 mm smaller than designed	Model holes slightly oversize, or ream them after printing
Holes printed sideways (axis parallel to the bed)	Typically slightly oval, with a flatter top	Use a teardrop shape or orient the hole vertically if roundness matters
Faces on the build plate	Typically the flattest, most accurate surface	Put locating faces down where you can
Long, flat parts	Can warp slightly in some materials	Add ribs, or choose a low-warp material

If a dimension really matters, tell us which one when you order. We can dial it in, and on request we'll send photos and a dimension check of the finished part before pickup or shipping.

Clearances for Common Fits

Clearance is the gap between two mating parts. The values below are typical starting points for FDM, given per side (so a 10 mm pin in a hole for a slip fit would start with a hole of about 10.4–10.6 mm). They assume holes printed vertically. Add the 0.1–0.2 mm hole undersize on top if you want a margin.

Fit	Typical clearance per side	Use for
Press fit	0 to 0.1 mm	Pins, bearings and parts that should stay put
Snug or location fit	0.1–0.2 mm	Parts that locate firmly but can be pulled apart
Slip or sliding fit	0.2–0.3 mm	Lids, sliders, parts that move by hand
Loose or running fit	0.3–0.5 mm	Hinges, rotating parts, print-in-place mechanisms

For anything important, print a small test coupon with a few clearance steps first. It costs little and tells you exactly which gap works for your material and geometry.

Snap Fits

Snap fits work in FDM, but material and orientation make or break them.

• Material: PETG and nylon are the best choices. They flex without snapping. PLA is brittle under repeated flexing. PPA-CF and PPS-CF are stiff and brittle, so snap-fits in them can crack.
• Orientation: print the cantilever arm so it bends along the layers, not across them. An arm that flexes across layer lines tends to snap at the root.
• Root radius: add a fillet where the arm meets the body. Sharp roots concentrate stress.
• Length: longer, thinner arms flex more gently than short, thick ones.

Wall Thickness

Wall	Result
Under 0.4 mm	Won't come out in the print
0.8 mm	Minimum; prints, but fragile
1.2 mm	Recommended for most parts
1.6–2.0 mm	Strong, functional parts

Thicker is not always better. Very thick solid sections add weight, print time and cost. Use ribs and infill instead. Our guides to infill and reducing print costs explain how.

Overhangs, Bridges and Supports

• Overhangs steeper than about 45° from vertical need supports.
• Short bridges between two points typically print cleanly without supports; long ones sag.
• Supports leave marks and add material, so design them out where you can with chamfers instead of flat ceilings.
• PETG bonds strongly to its own supports, which makes them harder to remove cleanly.
• TPU supports are very difficult to remove, so design flexible parts to print without them.

Threads and Fasteners

Thread size	Best option
M6 and larger	Printed threads work well
Smaller than M6	Heat-set brass inserts, or self-tapping screws into a pilot hole
Parts that come apart often	Heat-set inserts with machine screws

Size insert pockets to the insert maker's recommendation, and leave at least 1.6–2.0 mm of wall around them.

Build Size

Our printers build parts up to approximately 325 × 320 × 325 mm in one piece. Larger items can be split into sections that bolt or glue together. Design the split with alignment pins or a lap joint so the halves line up. Message us on Telegram to confirm size limits for a specific project.

Material Limits at a Glance

Heat resistance figures are approximate and come from our materials pages. Treat them as the upper limit, not a comfortable working temperature.

Material	Heat resistance	Design notes
PLA	~55–60 °C	Excellent dimensional accuracy and low warping; brittle under impact
PETG	~80 °C	Tough with a little flex; good for snap fits
ASA	~100 °C	UV-stable for outdoor parts; prone to warping without an enclosure
Nylon	~90 °C	Tough and wear-resistant; absorbs moisture
Polycarbonate	~120 °C	Very strong; significant warping tendency
TPU	~80 °C	Flexible; dimensional accuracy varies, so allow extra clearance
PA-CF	~150 °C	Stiff; much less warping than plain nylon
PAHT-CF	~180 °C	Dimensionally stable in heat and humidity
PPA-CF	Past 200 °C	Stiffest we offer; more brittle than nylon
PPS-CF	~260 °C	Very low moisture absorption, holds tolerances; brittle, best for static parts

All our printers have heated chambers, so warp-prone materials like ASA and PC are printed properly in-house. Large flat parts in these materials still benefit from ribs and rounded corners.

Pre-Upload Checklist

• Walls at least 1.2 mm, or 1.6–2.0 mm for functional parts
• Holes modelled with the 0.1–0.2 mm undersize in mind
• Clearances chosen for each fit, with a test coupon for critical ones
• Snap-fit arms in PETG or nylon, flexing along the layers
• Threads under M6 swapped for inserts
• Overhangs over 45° supported or redesigned
• Part within 325 × 320 × 325 mm, or split with alignment features
• Units checked (a model exported in inches arrives 25.4 times too small)

Every file also gets our free file check before it goes on a printer. We look at wall thickness, tolerances, clearances, orientation and supports, and suggest fixes.

Quick FAQ

How accurate are FDM parts?

Typically ±0.2–0.5 mm, with holes coming out 0.1–0.2 mm smaller than designed.

What is the thinnest wall you can print?

0.8 mm is the minimum and fragile. 1.2 mm is recommended for most parts. Anything under 0.4 mm won't print.

Can you print small screw threads?

Printed threads work best at M6 and larger. For smaller sizes, use heat-set brass inserts or self-tapping screws.

What clearance should I use for a sliding fit?

Start at about 0.2–0.3 mm per side and test. The best value depends on the material and the shape.

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