Split Lock Washer
Washers · helical spring washer · spring lock washer
Definition: A split lock washer is a helical, split ring that acts as a spring to add tension against the nut or bolt head, intended to resist vibration loosening.
Anatomy
■ Body■ Hole
Governing standards: ASME B18.21.1
Common Sizes
| Inch | Metric | Head width | Head height |
|---|---|---|---|
| 1/4 | M6 | 1/2 OD | 0.09 |
| 3/8 | M10 | 11/16 OD | 0.13 |
| 1/2 | M12 | 7/8 OD | 0.17 |
Representative sizes. Full dimensional data lives in the standards listed below.
Grades & Strength
| Grade | Material | Tensile (psi) | Marking |
|---|---|---|---|
| Zinc steel | carbon steel, zinc-plated | — | None |
| Stainless | 304 stainless | — | None |
Materials
- Zinc-plated steel
- Stainless steel
- Phosphor bronze
Pros & Cons
Pros
- Cheap, one-piece anti-loosening attempt
- Works where a lock nut will not fit
- Widely available
Cons
- Effectiveness is debated — modern tests show limited benefit
- Can damage soft surfaces and coatings
- Less reliable than a nyloc or threadlocker
Typical Uses
- Vibration-prone equipment
- General bolted assembly
- Applications where a lock nut is impractical
Alternatives & Related
- Lock Nut — More reliable anti-vibration locking
- Flat Washer — Load spreading without the spring effect
Where to Buy
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FAQ
Do split lock washers actually work?
Modern testing (including NASA and Junker tests) shows they provide little protection once the joint is fully tensioned. For real vibration resistance, use a nyloc nut, threadlocker, or a properly preloaded joint.
Where does a lock washer go — nut side or bolt side?
Traditionally under the nut (the side that turns), but since preload matters more than position, place it under whichever side you are tightening.