What Is a Fish Plate in Railway?
A fish plate, also known as a joint bar or splice bar, is a steel bar bolted to the ends of two adjacent rails in a railway track to join them together. It is a structural connector that re-establishes effective sectional strength at the rail joint, allowing jointed track to withstand repeated axle loading without excessive deformation. The fish plate ensures structural continuity, stability and proper alignment of the rail ends, prevents vertical or lateral deflection under passing trains, and leaves a controlled gap so the rails can expand and contract with temperature changes.
Key Functions of Fish Plates
Fish plates perform several critical duties in jointed track. They hold the two rail ends firmly in position and transfer the vertical wheel load from one rail end to the other across the joint. They restrain the rail ends against vertical and lateral movement so the running surface stays level and the gauge stays constant. They allow thermal expansion and contraction of long rail strings through the designed joint gap, and they maintain electrical and structural continuity where required by the signalling system. In plain jointed track, the fish plate is the component that keeps the joint safe at the operating speed of the line.
Main Types of Rail Joints
| Joint Type | Key Specification and Description |
|---|---|
| Standard Rail Joint Fish Plate | Profile matches the rail section such as UIC 60 or 136RE; length typically 600 mm or 800 mm per side; 4 or 6 bolt holes per bar |
| Insulated Rail Joint | Steel core with composite insulating end posts and plates, or full epoxy composite; electrical resistance above 10 to the power of 8 ohm |
| Compromise Rail Joint | Connects two different rail profiles such as UIC 54 to UIC 60; each side is machined to match its own rail section |
| Joggled Rail Joint | Has a depressed section to keep a continuous rail head surface for smoother wheel passage |
| Bridge Rail Joint | Reinforced with thicker web or longer length for high-stress locations such as bridge approaches |
| Glued Insulated Joint | Steel bars bonded to composite insulation with high-strength adhesive for improved durability |
| Expansion Joint for BRE | Allows controlled thermal movement in long rails on bridges or in extreme temperature zones |
Typical Specifications by Standard
Railway fish plates are specialised steel components that connect rail ends and are designed to meet specific standards for strength and fit according to the rail weight and application. They are typically 600 to 1200 mm in length and 20 to 32 mm thick, feature 4 or 6 holes, and are manufactured from high-strength steel with 550 to 900 MPa tensile strength to ensure structural integrity. Common standards include AREMA, BS, UIC, DIN, GB, JIS and AS. The table below shows representative fish plate data.
| Standard | Rail Type | Length and Hole | Weight | Material |
|---|---|---|---|---|
| AREMA | 115RE | 4 hole, 24 inch | 17.04 kg | 45# steel, C 0.42-0.50, Mn 0.50-0.80 |
| AREMA | 132-136RE | 6 hole, 36 inch | 26.63 kg | 45# steel, Si 0.17-0.37, Cr max 0.25 |
| UIC 864 | UIC 60 | 4 hole, 630 mm, hole 26 mm | 18.07 kg | P max 0.035, S max 0.035 |
| UIC 864 | UIC 54 | 6 hole, 800 mm | 19.94 kg | Per standard composition |
| BS 47-1 | BS 75R | 4 hole | 6.56 kg | Per standard composition |
| BS 47-1 | BS 90A | 685.8 mm, hole 26 mm | 13.23 kg | 50# steel |
| AS | 50 kg | 4 hole | 14.30 kg | Per standard composition |
| DIN | S49 | 4 hole | 9.71 kg | Per standard composition |
Design, Quality and Common Misconceptions
The surface of the fish plate must be clean and smooth with no cracks, crusting or scratches, and the end faces must be free of shrinkage marks and interlayers. The upper and lower shoulders of the plate must make close contact with the rail web and foot so the load is transferred evenly when a train passes. Because the joint area is subjected to complex stresses including bending, shearing and fretting wear, heat treatment is applied during production to guarantee consistent hardness and durability across the whole plate.
One misconception is that a fish plate simply holds two rails together and carries no load. In reality the plate is a load-bearing structure that restores bending strength at the joint. Another misconception is that all joint bars are interchangeable; each rail section needs a plate with a matching profile, hole pattern and length. It is also often assumed that longer plates are always stronger, but the correct length depends on the rail section, the sleeper spacing and the required joint stiffness for the line speed.
Frequently Asked Questions
What is the use of a fish plate in railway? fish plate joins the ends of two rails, restoring sectional strength at the joint and keeping the rails aligned, stable and level under traffic.
How long is a typical fish plate? Fish plates are usually 600 to 1200 mm long and 20 to 32 mm thick, with 4 or 6 bolt holes per bar.
What is an insulated rail joint? It is a joint with composite insulating parts that electrically separates two rail sections while carrying the mechanical load, with resistance above 10 to the power of 8 ohm.
Which standards cover rail fish plates? Common standards include AREMA, UIC 864, BS 47-1, DIN, GB, JIS and AS.
What is a compromise joint bar? It is a fish plate that connects two different rail profiles, with each side machined to match its respective rail section.
Why must fish plate surfaces be defect free? Cracks, crusting or scratches create stress concentration points that can lead to fatigue failure at the joint under repeated wheel loads.
