A fish bolt is a rail fastener used together with a rail joint or fish plate to connect two rails end-to-end. Many types of fish bolts are available on the railway material market, and choosing correctly matters because the joint is one of the weakest points of the track. This article compares common fish bolts and high-strength fish bolts to help buyers select the right product.
What Is a Fish Bolt
A fish bolt passes through the bolt holes of a fish plate and the rail web, and is tightened with a nut to clamp the joint together. It transfers load across the joint and keeps the rail ends aligned. The bolt must be strong enough to resist shear forces and fatigue from passing wheels, and its material and strength grade determine the service life of the joint.
Ordinary vs High-Strength Fish Bolts and Strength Grades
Common fish bolts are usually made of Q235 carbon steel and are used in secondary structures and light lines. High-strength fish bolts are made of high-strength steel, such as 45 steel, 40 boron steel, 20 manganese titanium boron steel or 35CrMoA, and are heat treated by quenching and tempering. They are designed to withstand loads greater than ordinary bolts of the same specification and are mostly used for the connection of bridges and steel rails on busy lines.
| Aspect | Ordinary Fish Bolt | High-Strength Fish Bolt |
|---|---|---|
| Typical material | Q235 | 45#, 40B, 20MnTiB, 35CrMoA |
| Strength grade | 4.8, 5.8, 6.8 | 8.8, 9.8, 10.9, 12.9 |
| Load transfer | Shear of bolt rod, hole wall pressure | Pre-tension and friction between plates |
| Reuse | Can be reused | Generally not reusable |
| Typical use | Secondary structures, light lines | Main lines, bridges, heavy traffic |
Strength grades indicate the mechanical capacity of the bolt. Ordinary fish bolts are commonly supplied in grades 4.8, 5.8 and 6.8, while high-strength fish bolts are supplied in grades such as 8.8, 9.8, 10.9 and 12.9, of which 10.9 is very common in railway joint applications. The grade number relates to tensile and yield strength; a 10.9 bolt, for example, provides much higher pre-tension capacity than a 4.8 bolt.
Insulated Fish Bolts
Insulated fish bolts are used in insulated rail joints to fasten steel rails while maintaining electrical isolation for track circuits. They combine high strength with insulating sleeves and washers, and are installed with the same torque discipline as standard high-strength bolts. They are a specialized variant, not an alternative to ordinary fish bolts, and should be selected when signalling isolation is required at the joint.
Selection Checklist
When choosing a fish bolt, check the rail section and fish plate hole diameter, the required strength grade based on traffic and bridge conditions, the material and heat treatment, the corrosion protection suitable for the environment, and the applicable standard. Confirm whether the joint needs insulation. For high-strength bolts, plan controlled torque tightening with a calibrated wrench, and do not reuse bolts after removal.
Common Misconceptions
A common mistake is treating all fish bolts as interchangeable; strength grade and material directly determine joint capacity and fatigue life. Another is reusing high-strength fish bolts after disassembly; they are pre-stressed fasteners designed for permanent connections and should be replaced. Ordinary fish bolts, by contrast, can generally be re-tightened and reused on secondary lines.
Frequently Asked Questions
What is the difference between ordinary and high-strength fish bolts? Material, strength grade and working principle: high-strength bolts use pre-tension and friction, while ordinary bolts rely on shear resistance.
What strength grades are available for high-strength fish bolts? Grades such as 8.8, 9.8, 10.9 and 12.9, with 10.9 being common in railway joints.
What material are ordinary fish bolts made of? Typically Q235 carbon steel, suitable for secondary structures and light lines.
Can high-strength fish bolts be reused? No. They are pre-stressed fasteners for permanent connections and should be replaced after removal.
When is an insulated fish bolt needed? t insulated rail joints where electrical isolation for track circuits is required.
