An M4 bolt is 4.00 mm (0.157") in diameter. The nearest stocked inside diameter is 3/16" (4.76 mm) — a clearance fit that slides on easily and seats flat under the bolt head. Every size below ships in Neoprene, EPDM, Nitrile, Silicone, Natural Rubber, Viton and Fiber.
Best in-stock matches for M4
| Washer size | Fit |
|---|---|
| 1/2" OD × 3/16" ID × 1/16" | Compact, general purpose |
| 5/8" OD × 3/16" ID × 1/16" | Wider sealing face |
| 3/4" OD × 3/16" ID × 1/8" | Fender-style, more compression |
| 1" OD × 3/16" ID × 1/8" | Maximum coverage |
Browse every 3/16" ID rubber washer for more OD and thickness options.
Sizing note
Rubber compresses 20–30% under proper torque, so the 0.76 mm of clearance disappears the moment you tighten down. For a snugger hole fit on M4, there is no smaller stocked ID — 3/16" is the correct choice.
More metric bolts: M5 · M6 · M8 · M10 · M12 · M16 · M20 — or see the full metric conversion guide, use the Size Finder, or open the complete size chart.
FAQ
What size rubber washer fits an M4 bolt?
A 3/16" (4.76 mm) inside diameter rubber washer is the stocked match for a 4 mm M4 bolt, giving an easy clearance fit that seals flat when tightened.
What OD should I pick for M4?
1/2" OD suits tight spaces; 3/4"–1" OD spreads load and seals larger holes, fender-washer style.