Holes
Minimum hole diameter:
FDM: 2.0mm (smaller holes tend to close up)
SLA: 2.0mm (high detail capability)
Industrial SLA: 2.0mm (high detail capability)
MJF: 1.5mm (powder must be able to escape)
Compensation: Holes in 3D printed parts tend to print slightly smaller than designed due to material shrinkage and over-extrusion. Add 0.1–0.2mm to the radius for FDM, or 0.05–0.1mm for SLA.
Orientation matters: Holes printed vertically (along Z-axis) are more accurate and round. Holes printed horizontally may be slightly oval and need support material inside.
Threads
Printed threads are possible but have limitations:
Minimum thread size: M6 for FDM, M3 for SLA
Coarse threads (e.g., M6x1.0) work better than fine threads
Threads printed vertically are more accurate
Printed threads wear out faster than metal threads
Better alternatives to printed threads:
Heat-set threaded inserts — Brass inserts pressed into the plastic with a soldering iron. Strong, reusable, professional. Design a hole slightly smaller than the insert’s outer diameter.
Self-tapping screws — Design a pilot hole and let the screw cut its own thread. Works well in Nylon and ABS.
Tap after printing — Print an undersized hole and tap it with a standard thread tap. Best for larger threads (M5+).
Heat-set insert design guidelines
Hole depth: insert length + 1mm
Hole diameter: insert outer diameter minus 0.2–0.8mm (material melts around it)
Wall thickness around insert: minimum 2x the insert diameter
Leave 2mm+ clearance from the bottom of the hole to the opposite wall
Assembly clearances
For parts that need to fit together, per side (the gap on each side of the joint):
Press fit: 0.1–0.15mm on FDM, 0–0.1mm on MJF, 0–0.05mm on SLA
Slip fit (goes together by hand and stays put): 0.2–0.3mm on FDM and MJF, 0.125–0.2mm on SLA
Moving fit (hinges, sliders): 0.3–0.4mm on FDM and MJF, 0.2–0.3mm on SLA
For a pin in a hole, make the hole larger than the pin by twice the figure. Full table, including Industrial SLA, FGF and TPU: What clearance should I give two fitting parts?
For critical assemblies, order a test print first to validate fit before committing to a full order.
Makelab is a professional 3D printing service in Brooklyn, NYC. Our engineers review every file for printability and can help optimize your design. Get an instant quote.
Learn more on our website:
Full Design Guidelines — comprehensive rules by technology
File Requirements — formats, mesh settings, export tips
Browse Materials — find the right material for your application
How do I design for threaded inserts or assembly?
Designing parts with threaded inserts or assembly features requires planning for manufacturing and functionality:
Threaded inserts (recommended method)
Heat-Set Inserts — Design holes 0.1-0.2mm smaller than insert outer diameter. Inserts are pressed in with a soldering iron after printing. Provides strong, reusable metal threads. Best for repeated assembly/disassembly and high-load applications.
Press-Fit Inserts — Design holes slightly undersized for interference fit. Insert pressed in manually or with arbor press. Good for lower-load applications and permanent assemblies.
Design tips for inserts
Add chamfers to hole openings for easier insertion
Provide at least 3-4mm of material depth around the insert
Orient holes vertically (Z-axis) during printing for best results
Printed threads (not recommended)
Printing threads directly is possible but:
Weak and prone to stripping
Requires post-processing (tapping) for reliability
Only suitable for very low-load, occasional use
Assembly features
Snap-Fit Joints — Use flexible materials like PETG or Nylon. Design with 15-20° lead-in angles. Account for material deflection.
Alignment Features — Add pins and corresponding holes for precise alignment. Use the slip-fit clearance per side: 0.2–0.3mm for FDM and MJF, 0.125–0.2mm for SLA.
Interlocking Parts — Give mating surfaces at least the slip-fit clearance per side: 0.2mm on FDM and MJF, 0.125mm on SLA. Test fit with a prototype before final production.
👉 Need help designing assembly features? Submit the intake form and our team can provide guidance.
Can you print threaded holes or inserts?
Yes — threaded features can be integrated, but design and process must be considered.
Small threads are often tapped post-print for strength and accuracy. Heat-set inserts are also commonly used for durability in nylon parts. Directly printing threads may not be reliable for repeated use.
👉 To confirm the best approach for threads, submit the intake form with your file and application details.