--- title: "Tolerances and clearances for 3D printed fits" description: "How much clearance to leave for press fits, sliding fits, snap fits, lids and bearings on an FDM printer, and how to describe them so SpeakCAD gets the fit right first time." canonical: https://speakcad.com/guides/tolerances-and-clearances published: 2026-09-03 updated: 2026-09-03 publisher: SpeakCAD --- # Tolerances and clearances for 3D printed fits > How much clearance to leave for press fits, sliding fits, snap fits, lids and bearings on an FDM printer, and how to describe them so SpeakCAD gets the fit right first time. Tolerance is the difference between a part that fits and a paperweight. Printers vary, but FDM behaviour is predictable enough that a few rules cover most cases. ## Start with your printer's real number Print a 20 mm cube and a 10 mm hole test. If the cube is 20.2 and the hole is 9.7, your printer adds about 0.2 mm per side on outer walls and removes about 0.3 mm from holes. Most well-tuned machines land near these values, and SpeakCAD's defaults assume them. ## Clearance table (per side, FDM, PLA/PETG) | Fit | Clearance | Use | |---|---|---| | Press fit (no movement) | 0.1 to 0.2 mm | Pegs, bearings, magnets | | Light press / snug | 0.2 to 0.3 mm | Lids that should stay on, knobs on D-shafts | | Sliding fit | 0.4 to 0.6 mm | Drawers, sliding lids, pistons | | Free / loose | 0.8 mm+ | Hinges, hanging parts | | Printed threads | 0.3 to 0.4 mm on the profile | M8 and larger | ## Snap fits A cantilever clip with 0.2 mm of interference and a 45° lead-in engages firmly in PLA and PETG. Longer arms flex more: aim for an arm length at least 6 times its thickness. Print arms lying flat so the bend is along the layers. ## Bearings and magnets 608 bearings (22 mm outer) go into a 22.2 mm pocket for a firm press. 6 mm round magnets fit a 6.2 mm hole. Add a 0.3 mm chamfer at the mouth to guide them in. ## Shafts and bores A 6 mm shaft that must not spin in a knob: 5.9 to 6.0 mm bore plus a flat matching the D profile. A 6 mm shaft that must rotate freely: 6.4 to 6.6 mm bore. ## Test the fit before the full print The numbers above are averages. To find your printer's own number without measuring anything, use [Fit Check](/guides/fit-check-parts-that-fit-first-time): SpeakCAD cuts a five-minute slice of the fit from your model, you report too tight, perfect or too loose, and the clearance your printer needs is saved on your account for every later part. ## Describing fits to SpeakCAD Say what you want to happen, not just the number: "press fit on a 6 mm shaft", "lid slides on smoothly", "magnets 6 x 2 mm pressed in". The AI applies the clearance and states the final dimensions in its reply. If a test print is off, quote the measured gap and ask for the correction; re-downloading after a tolerance fix is free. ## About SpeakCAD SpeakCAD is the most intuitive CAD for 3D printing, made for people who own a 3D printer and need a part that fits something they have: tap a face and type a size to shape it with simple tools, or describe it to the AI, on your phone or computer, and download a print-ready STL, 3MF or G-code sliced for your printer. SpeakCAD works inside ChatGPT and Claude as a plugin (an MCP server): ask the assistant for a part with its measurements and SpeakCAD's own CAD AI designs it, shows it in 3D in the chat and hands over a print-ready STL, 3MF or G-code sliced for your printer. - Live demo, no account: https://speakcad.com/demo - In ChatGPT, Claude and other MCP clients: https://speakcad.com/chatgpt-plugin, https://speakcad.com/claude-connector, https://speakcad.com/mcp-server - Pricing: https://speakcad.com/pricing - FAQ: https://speakcad.com/faq - Site index for AI assistants: https://speakcad.com/llms.txt