Product Specifications
| Model / Specification | M17 – M23 |
| Material | Carbon Steel |
| Size | 17 | 21 | 23 | |
| d | Nom. | 17 | 21 | 23 |
| Max. | 17.5 | 21.5 | 23.5 | |
| Min. | 16.7 | 20.5 | 22.5 | |
| dc | 27 | 33 | 35 | |
| b | Nom. | 5 | 6 | 6 |
| Max. | 5.2 | 6.2 | 6.2 | |
| Min. | 4.8 | 5.8 | 5.8 | |
| h | Nom. | 7 | 8 | 8 |
| Max. | 8.05 | 9.05 | 9.05 | |
| Min. | 5.95 | 6.8 | 6.8 | |
| s | Nom. | 3.5 | 4 | 4 |
| Max. | 3.7 | 4.2 | 4.2 | |
| Min. | 3.3 | 3.8 | 3.8 | |
Spring Lock Washer for Railway Track Rail Fastener / Rail Bolt — Product Introduction
UNI 3558-1959 is a technical specification in Italian railway standards for spring lock washers used with rail bolts, primarily applied in railway track fastening systems. These washers are typically manufactured from spring steel, commonly using materials such as 55Si7 (equivalent to 60Si2Mn) or 51CrV4 (equivalent to 50CrVA), treated by quenching and tempering, with general hardness of HRC 42–50. They feature a single-coil split (open) spring washer design, installed in rail bolt connection pairs, and rely on elastic deformation and frictional resistance to prevent bolt loosening under train-induced vibration — making them a critical anti-loosening component in railway track fastener systems.
I. Product Features
- High-strength spring steel construction: Made from premium spring steel with excellent elasticity and toughness, capable of withstanding repeated loading.
- Elastic anti-loosening structure: The split design generates axial spring force under bolt preload, continuously providing anti-loosening torque.
- Excellent fatigue resistance: With proper heat treatment, it offers strong fatigue resistance, suitable for long-term vibration conditions of railway lines.
- Dimensions compliant with railway standards: Manufactured to UNI 3558-1959, matching corresponding rail bolts and nuts with good interchangeability.
- Diverse surface protection options: Common surface treatments include oxidation (blackening), phosphating, or zinc-plated passivation for improved corrosion resistance.
II. Product Advantages
- Reliable anti-loosening performance: The spring washer’s bevel (slant gap) and elastic deformation effectively suppress bolt loosening under vibration and impact, ensuring track connection safety.
- Adapted to harsh railway environments: Fatigue-resistant and impact-resistant, suitable for exposed, humid railway line conditions with large temperature variations.
- Easy maintenance: Simple structure, easy installation and removal, straightforward inspection and replacement, reducing track maintenance costs.
- High standardization: Conforms to UNI 3558-1959, facilitating selection and replacement for international railway projects or lines adopting Italian standards.
- Protects the connection pair: To a certain extent, distributes loads and reduces damage to mating components caused by bolt heads or nuts.
III. Applications
The UNI 3558-1959 spring lock washer for rail bolts is primarily suitable for:
- Railway track fastener systems: Bolt connections between rails, sleepers, and baseplates.
- Switch and crossing fastening: Anti-loosening of bolts in critical areas such as switch mechanisms and frog sections.
- Bridge guard rails and line auxiliary equipment: Fastening connections for guard rails, anti-creep devices, and rail gauge rods.
- Other track fastening systems adopting UNI 3558-1959: Particularly suitable for Italian standard systems or lines using related imported technology.
- Heavy-haul, high-speed, and conventional railway lines: Capable of meeting anti-loosening requirements for rail bolts across different railway classes.
