Prevailing Torque Lock Nut
Nuts · stover nut · distorted thread nut · all-metal lock nut · conelock nut
Definition: A prevailing torque lock nut has deformed or pinched threads that grip the bolt, resisting loosening without a nylon insert — so it survives heat.
Anatomy
■ Body■ Internal thread
Governing standards: ASME B18.16.6 · ISO 7042 · DIN 980
Common Sizes
| Inch | Metric | Head width | Head height |
|---|---|---|---|
| 1/4-20 | M6 | 7/16 | 1/4 |
| 3/8-16 | M10 | 9/16 | 5/16 |
| 1/2-13 | M12 | 3/4 | 3/8 |
Representative sizes. Full dimensional data lives in the standards listed below.
Grades & Strength
| Grade | Material | Tensile (psi) | Marking |
|---|---|---|---|
| Grade 5 | medium carbon steel, Q&T | 120,000 | 3 radial lines |
| Grade 8 | alloy steel, Q&T | 150,000 | 6 radial lines |
Materials
- Zinc-plated steel
- Stainless steel
- Alloy steel
Pros & Cons
Pros
- All-metal — no temperature limit like nylon
- Locks at any position on the thread
- Reusable several times
Cons
- More drag to run down
- Locking torque fades with reuse
- Costs more than a plain hex nut
Typical Uses
- Exhaust systems
- Engine and transmission
- High-temperature machinery
- Aerospace
Alternatives & Related
- Nylon Lock Nut — Nylon insert where heat is not a factor
- Flange Nut — Built-in washer face plus serrations
- Castle Nut — Positive mechanical lock with a cotter pin
Where to Buy
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FAQ
What is a prevailing torque nut?
A lock nut whose threads are deliberately deformed so they clamp the bolt at any position — it resists loosening by friction, not by a plastic insert.
Can you reuse prevailing torque nuts?
A few times, but the locking torque fades with each use. Replace them in safety-critical or high-vibration joints.