The rule that sets rivet diameter: 3 times the thickness
The shank should be at least three times the thickness of the thickest sheet you are joining. Two 2 mm sheets means a minimum 6 mm rivet, rounded up to the nearest stock size. Bigger is not safer: an oversize rivet needs an oversize hole, which weakens the material. If you need more strength, use more rivets, not larger ones.
Standard rivet sizes and grip guide
| Material thickness | Min. diameter (3t) | Nearest stock size |
|---|---|---|
| 0.5–1 mm | 1.5–3 mm | 2–3 mm (1/16–1/8") |
| 1–2 mm | 3–6 mm | 3–4 mm (1/8–5/32") |
| 2–3 mm | 6–9 mm | 6.4–8 mm (1/4–5/16") |
| 3–4 mm | 9–12 mm | 10 mm (3/8") |
Metric stock runs 2, 2.4, 3, 3.2, 4, 4.8, 5, 6.4, 8, 10 mm; US sizes step in 1/32". For material thicker than 8 mm, switch to Unwin's rule: diameter = 6.05√t in mm.
Length, hole and material pairing
- Length. L = total grip + 1.5D. Joining a 4 mm stack with a 6 mm rivet needs 4 + 9 = 13 mm of length.
- Hole. Drill the rivet diameter plus 0.08 mm (0.003"), just enough clearance to insert before setting.
- Count layers, not sheets. Grip is every layer added together. Sheet + wood + sheet is three thicknesses.
- Match the metals. A steel rivet in aluminum (or vice versa) sets up galvanic corrosion. Use a neutral rivet like stainless, or isolate the joint.
Common questions
What size rivet do I need for 3 mm material?
Use the rule diameter equals 3 times the thickest layer, so 3 mm needs about a 9 mm rivet. Round up to the next stock size, which is 10 mm metric or 3/8 inch. For light loads an 8 mm rivet is usually fine.
How do I work out rivet length?
Length equals total grip (the combined thickness of all layers) plus 1.5 times the rivet diameter. That extra 1.5D is the material needed to form the second head. Too short and the head will not form; too long wastes stock and buckles.
Should I drill the hole exactly the rivet diameter?
Drill it slightly larger so the rivet slides in before it is set: about +0.08 mm, or +0.003 inch. A hole too tight risks splitting the material; too loose lets the rivet tilt and weakens the joint.
