Nylon vs All-Metal Lock Nuts Comparison
Quick Answer
Use nylon insert lock nuts for:
- General vibration resistance
- Temperatures below 120°C (250°F)
- Cost-sensitive applications
- Most industrial applications
- Consistent prevailing torque needed
Use all-metal lock nuts for:
- High temperature (above 120°C)
- Chemical exposure
- Frequent reuse required
- Extreme vibration
- Food/pharmaceutical (no plastic contamination)
Specification Comparison
| Feature | Nylon Insert | All-Metal |
|---|---|---|
| Max Temperature | 120°C (250°F) | 300-425°C (570-800°F) |
| Min Temperature | -40°C (-40°F) | -50°C (-60°F) |
| Reuse Cycles | 3-5 (limited) | 10-15+ |
| Prevailing Torque | Consistent | More variable |
| Chemical Resistance | Limited | Excellent |
| Cost | Lower | Higher |
| ISO Standard | ISO 10511 (thin), ISO 10512 | ISO 7040 (thin), ISO 7042 |
| DIN Standard | DIN 985 (thin), DIN 982 | DIN 980, DIN 6925 |
How Each Type Works
Nylon Insert Lock Nuts
1. Bolt threads push into nylon insert
2. Nylon deforms to grip threads
3. Friction prevents loosening
4. Locking is purely mechanical
All-Metal Lock Nuts
1. Top threads are slightly deformed (oval/crimped)
2. Bolt forces threads back to round
3. Metal-to-metal friction locks
4. No plastic components
Temperature Comparison
| Temperature Range | Nylon Insert | All-Metal | Notes |
|---|---|---|---|
| Below -40°C | Nylon brittle | ✓ Works | Extreme cold |
| -40°C to 100°C | ✓ Optimal | ✓ Works | Normal service |
| 100°C to 120°C | ✓ Max limit | ✓ Works | Nylon limit approaching |
| 120°C to 150°C | ❌ Nylon fails | ✓ Works | Above nylon rating |
| 150°C to 300°C | ❌ | ✓ Works | All-metal required |
| Above 300°C | ❌ | ⚠️ Verify grade | Special materials |
What Happens to Nylon at High Temperature?
- Softens and loses grip
- Melts (~260°C for PA6/nylon 6)
- Prevailing torque drops to zero
- Nut becomes standard (non-locking)
Reusability Comparison
| Usage Cycles | Nylon Insert | All-Metal |
|---|---|---|
| 1-3 | Full effectiveness | Full effectiveness |
| 4-5 | Reduced, inspect | Full effectiveness |
| 6-10 | Replace | Good, check torque |
| 11-15 | — | Reduced, inspect |
| 15+ | — | Replace |
Why Nylon Has Limited Reuse
- Nylon is cut/deformed by bolt threads
- Each cycle damages the nylon more
- Thread path becomes worn
- Grip force decreases measurably
Why All-Metal Lasts Longer
- Metal deformation is more elastic
- Less material removal per cycle
- Can be re-deformed slightly during tightening
- Higher initial strength
Prevailing Torque Comparison
Nylon Insert
| Size | Min Prevailing | Max Prevailing |
|---|---|---|
| M6 | 0.5 Nm | 3.0 Nm |
| M8 | 0.8 Nm | 5.0 Nm |
| M10 | 1.2 Nm | 7.5 Nm |
| M12 | 1.5 Nm | 10 Nm |
Characteristics: Very consistent, predictable, smooth
All-Metal
| Size | Min Prevailing | Max Prevailing |
|---|---|---|
| M6 | 1.0 Nm | 7 Nm |
| M8 | 2.0 Nm | 14 Nm |
| M10 | 3.5 Nm | 24 Nm |
| M12 | 5 Nm | 36 Nm |
Characteristics: Higher but more variable, may feel "sticky"
Cost Comparison
| Factor | Nylon Insert | All-Metal |
|---|---|---|
| Material cost | Lower | Higher |
| Manufacturing | Simpler | More complex |
| Typical price | 1× (baseline) | 1.5-2× |
| Stainless versions | 1.5× | 2-3× |
Volume consideration: For large quantities in acceptable environments, nylon saves significant cost.
Chemical Resistance
| Chemical | Nylon Insert | All-Metal |
|---|---|---|
| Oils/lubricants | Good | Excellent |
| Solvents (mild) | Fair | Excellent |
| Solvents (aggressive) | Poor | Excellent |
| Acids (dilute) | Poor | Good* |
| Alkalis | Poor | Good* |
| Salt water | Good | Good* |
| Fuels | Fair | Excellent |
*Depends on metal grade. Stainless provides better chemical resistance.
Chemicals That Attack Nylon
- Strong acids
- Phenols
- Certain chlorinated solvents
- Zinc chloride solutions
- Calcium chloride (in high concentration)
Application Guide
Use Nylon Insert Lock Nuts For:
| Application | Why Nylon Works |
|---|---|
| Automotive (interior, body) | Below 120°C, cost-effective |
| Appliances | Normal temperatures |
| HVAC equipment | General vibration, cost |
| Machinery (general) | Good performance, economical |
| Electronics enclosures | Adequate for service |
| Furniture | More than sufficient |
| Light industrial | Standard choice |
| Outdoor (non-extreme) | Good weather resistance |
Use All-Metal Lock Nuts For:
| Application | Why All-Metal Required |
|---|---|
| Engine/exhaust | High temperature |
| Brakes | High temp, safety-critical |
| Turbo/manifolds | Extreme heat |
| Chemical processing | Solvent exposure |
| Food processing | No plastic contamination |
| Pharmaceutical | Cleanroom, no particles |
| Aerospace | Extreme environments |
| Heavy mining/construction | Severe conditions |
| Cryogenic | Sub-zero operation |
| Frequent rebuild | Reusability important |
Vibration Resistance Comparison
Both types provide excellent vibration resistance when properly installed:
| Factor | Nylon Insert | All-Metal |
|---|---|---|
| Vibration resistance | Excellent | Excellent |
| NAS 3350 test | Pass | Pass |
| DIN 65151 test | Pass | Pass |
| Junker test | Pass | Pass |
Key point: When properly applied, both types prevent vibration loosening effectively. Choice depends on other factors (temperature, chemistry, reuse).
Thin vs Full Height
Both types come in two height versions:
Nylon Insert
| Type | Standard | Height | Use |
|---|---|---|---|
| Thin | ISO 10511 / DIN 985 | ~0.8d | General (most common) |
| Full | ISO 10512 / DIN 982 | ~1.0d | High strength required |
All-Metal
| Type | Standard | Height | Use |
|---|---|---|---|
| Thin | ISO 7040 / DIN 980 | ~0.8d | General (most common) |
| Full | ISO 7042 / DIN 6925 | ~1.0d | Critical, high strength |
Quick Decision Guide
Combination Strategies
For some applications, both types can be used strategically:
| Location | Nut Type | Reason |
|---|---|---|
| Near exhaust | All-metal | Heat |
| Near engine | All-metal | Heat + oil |
| Interior/body | Nylon | Cost, adequate conditions |
| Suspension | All-metal | Critical + severe duty |
| Trim/accessories | Nylon | Non-critical |
Installation Tips
Nylon Insert
- Run nut down slowly (don't burn nylon with friction)
- Feel for consistent resistance
- Don't reuse if resistance is low
- Torque to spec (don't rely only on prevailing torque)
All-Metal
- Expect higher installation torque
- May feel sticky or jerky — normal
- Can reuse if prevailing torque is still within spec
- Verify nut is not cross-threaded (harder to detect)
FAQ
Q: Can I use nylon lock nuts on my car's exhaust?
A: No. Exhaust temperatures far exceed 120°C. Use all-metal lock nuts or OEM-specified fasteners.
Q: Why did my nylon lock nut spin freely?
A: Either reused too many times, installed on damaged threads, wrong size, or exposed to heat/chemicals that degraded the nylon.
Q: Are all-metal lock nuts reusable indefinitely?
A: No, but significantly more than nylon. Check prevailing torque — if below spec, replace.
Q: Which is better for outdoor use?
A: Both work outdoors in normal temperatures. In extreme cold, all-metal is more reliable.
Q: Can I use lubricant with lock nuts?
A: Generally no — lubrication reduces prevailing torque and defeats the locking action. Install dry unless otherwise specified.
Q: Do I need a washer with lock nuts?
A: Not for locking function. Use washers for surface protection or load distribution if needed.
Choose nylon insert for general applications under 120°C, all-metal for high temperature, chemical exposure, or frequent reuse requirements.