Lock Washers
Washers & Retaining Rings · 8 specs
Direct Answer
Lock washers resist bolt loosening under vibration through spring preload and mechanical biting, standardized under DIN 127 (helical split spring washers), DIN 6798 (internal/external serrated tooth star washers), and DIN 2093 (Belleville conical spring discs).
Source: DIN 127-B / DIN 6798 / DIN 2093 / ASME B18.21.1 · Last reviewed Aug 28, 2026
Specs
| Governing Standards | DIN 127 Form B / DIN 6798 / DIN 2093 / ASME B18.21.1 |
| Helical Split Washer Mechanism | Spring tension + sharp trapezoidal edges that bite into mating surfaces under counter-rotation |
| M6 DIN 127 Split Lock Washer | ID: 6.1 mm | OD: 11.8 mm | Thickness (s): 1.6 mm | Uncompressed Free Height: ~3.2 mm |
| M8 DIN 127 Split Lock Washer | ID: 8.1 mm | OD: 14.8 mm | Thickness (s): 2.0 mm | Uncompressed Free Height: ~4.0 mm |
| M10 DIN 127 Split Lock Washer | ID: 10.2 mm | OD: 18.1 mm | Thickness (s): 2.2 mm | Uncompressed Free Height: ~4.4 mm |
| M12 DIN 127 Split Lock Washer | ID: 12.2 mm | OD: 21.1 mm | Thickness (s): 2.5 mm | Uncompressed Free Height: ~5.0 mm |
| Belleville Disc Spring (DIN 2093) | Conical shape maintains thousands of pounds of preload over high thermal expansion cycles |
| Serrated Tooth Star Washer (DIN 6798) | Multiple teeth bite through paint/anodizing to ensure electrical bonding and ground continuity |
Lock Washer Types & Anti-Vibration Performance Comparison
| Washer Type | Standard | Anti-Loosening Principle | Reusability | Critical Mechanical Limitations |
|---|---|---|---|---|
| Helical Split Spring | DIN 127-B / ASME B18.21.1 | Spring preload + split edge bite | Low (flattens permanently after 1–2 torques) | Ineffective above Grade 8.8 bolts (yields before bolt preloads) |
| Belleville Conical Disc | DIN 2093 | High-energy deflection cone (F propto delta) | High (spring steel 50CrV4) | High clamp load; excellent for thermal expansion joints |
| External Tooth Star | DIN 6798-A | Twisted radial teeth bite into head/joint | Single-use | Breaks paint for electrical chassis grounding |
| Internal Tooth Star | DIN 6798-J | Internal teeth enclosed under screw head | Single-use | Clean aesthetics; prevents snagging on small screws |
| Nord-Lock Wedge Pair | DIN 25201 | Wedge cams with angle alpha > beta (thread lead) | High (Multiple torque cycles) | Junker test verified: Only washer that mechanically prevents self-loosening |
The Junker Vibration Test & The Helical Split Washer Fallacy
Modern fastener engineering standards (NASA Reference Publication 1228 / DIN 25201) have largely superseded DIN 127 split spring washers for critical joints:
- The Junker Test Reality: Under transverse dynamic vibration, once a split lock washer is fully flattened by bolt pre-tension, it acts merely as a smooth hardened washer with a split. When joint movement begins, the split washer's edges can actually act as a ramp that accelerates fastener back-off.
- Where Wedge Locking / Nylocs Rule: For high-vibration applications (suspension, industrial pumps), engineering standards mandate Nord-Lock dual-wedge cam washers or DIN 985 prevailing-torque nylon insert lock nuts.