How to Design a Washer or Spacer
A washer or spacer is the simplest functional part there is — a flat ring or a short tube with a hole down the middle — which makes it a perfect thing to make yourself when the size you need isn’t in your parts bin. You only need three numbers: the inner diameter (the bolt passes through), the outer diameter, and the thickness (how far it spaces things apart). Here is how to pick each one.
The three dimensions
Inner diameter (ID)
The hole the bolt passes through. Use the clearance hole size for your bolt — a little bigger than the bolt shaft so it slides on. For an M3 that is about 3.4 mm.
Outer diameter (OD)
How wide the ring is. Bigger OD spreads the clamping load over more surface — useful on soft or 3D-printed parts so the bolt head doesn’t dig in.
Thickness / length
A thin disc is a washer; a longer tube is a spacer or standoff. This is just the gap you need to fill — measure it and match it.
Metric washer size chart (mm)
A practical starting point for flat washers by bolt size. The ID is a normal clearance hole; the OD and thickness follow common metric flat-washer proportions. Adjust the OD up if you want more bearing area.
| Bolt | Inner Ø (mm) | Outer Ø (mm) | Thickness (mm) |
|---|---|---|---|
| M3 | 3.4 | 7 | 0.5 |
| M4 | 4.5 | 9 | 0.8 |
| M5 | 5.5 | 10 | 1.0 |
| M6 | 6.6 | 12 | 1.6 |
| M8 | 9.0 | 16 | 1.6 |
The inner diameters come straight from the clearance-hole standard — the full table is in the metric clearance hole size chart. For a spacer, keep the same ID and OD and just set the thickness to the gap you need to fill.
Tips for 3D-printed washers and spacers
- Print flat. Lay a washer on its face so the layers run across the disc — it prints fast and won’t delaminate under clamping load.
- Oversize the hole slightly. Printed holes come out a touch undersized; add ~0.2 mm to the ID or the bolt may not pass. See 3D printed part tolerances.
- Tall spacers: a long, thin tube can tip while printing — add a small base or print a few at once for stability.
- Load-bearing? For real clamping force, a printed washer in tough filament (PETG, ABS) holds up better than brittle PLA — or print a wider OD to spread the load.
Make a custom washer or spacer
Tell PartWork.ai the three numbers — “a washer, 5.5 mm hole, 12 mm outer, 2 mm thick” or “an M3 standoff 10 mm tall” — and it builds the part. Check it in the 3D viewer, then export STL to print or STEP for a shop. See creating parts and exporting files.
Free to upload & view — sign up to download
Open the studio, describe the washer or spacer you need, and export a file ready to make. New accounts include free trial credits; more credits: 100 for $4.99 (~5¢ each).