What Is a Fishplate? Functions, Types and Materials of Rail Joint Bars

Why the Fishplate Matters at a Rail Joint

The rail joint is the most heavily loaded discontinuity in a track structure. A fishplate, also called a rail joint bar, is a steel section bolted to the web of two adjoining rails so that they behave as one continuous line. Its main function is to join the two rail ends, keep the running surface level and the gauge correct, and pass the wheel load from one rail to the next without letting the ends separate, shift or deflect.

Because the joint cannot match the stiffness of a continuous rail, the fishplate has to provide vertical and lateral stiffness locally, absorb impact and resist repeated thermal and dynamic movement over the whole service life of the track.

The Five Core Functions of a Fishplate

Connects the rails. It is bolted through the rail web with fish bolts, fastening two adjacent rail ends securely together.

Maintains alignment. It holds the rail table and the gauge consistent in both the horizontal and the vertical plane, so the running edge stays true.

Distributes load. It transfers the weight and dynamic forces of passing wheels across the joint and down into the sleepers.

Prevents separation. It stops the rail ends from spreading apart or creeping under thermal expansion, braking and traction forces.

Adds stability and insulation. It provides local stiffness that reduces impact and deflection, and in insulated designs it also breaks the electrical circuit for track signalling.

Types of Rail Joints and Fishplates

Ordinary rail joint

Made from general structural steel such as Q235, this is the standard joint used across most track. There are two common patterns, the 4-hole and the 6-hole fishplate, and the appearance and unit weight change with the rail weight of the line.

Insulated rail joint

The dimensions follow the ordinary joint, but the material and manufacturing process are set by the insulation standard. Insulated joints are installed at sections near power plants or on sections where stray current is a risk, and they prevent electrical leakage between track circuits.

Non-standard rail joint

These deviate from the ordinary fishplate because the rail section or the line speed demands it. Three variations are common: different weight, different bolt pitch and different external form.

Compromise rail joint

A compromise joint joins two rails of different sections or profiles. Typical examples include the bulge fishplate and the switch expansion joint. These are generally made to order for switch expansion joints and for alignment sections with special requirements, and they are the most demanding of the joint types to machine.

Typical Fishplate Models, Materials and Weights

Model	Material	Rail standard	Unit weight	Surface treatment
SJ50 rail joint	50# steel	50 kg/m rail	11.59 kg/pc	Plain
SJ43 rail joint	50# steel	43 kg/m rail	10.16 kg/pc	Plain
TJ57 rail joint	45# steel	57 kg/m rail	17.36 kg/pc	Plain
S30 rail joint	50# steel	Light rail section	5.8 kg/pc	Plain or as specified
CR135 rail joint	50# steel	CR135 crane rail	On request	Plain or hot-dip galvanized
CR171 rail joint	50# steel	CR171 crane rail	16.0 kg/pc	Plain or hot-dip galvanized
S49 forged rail joint	Q345	UIC49	8.60 kg/pc	Sandblasted and oiled
S60 forged rail joint	Q345	UIC60	14.50 kg/pc	Sandblasted and oiled

Stock programmes normally cover the 43 kg, 50 kg and 60 kg rail joints as well as heavy crane rail joints matched to sections such as CR73 and QU120, so that urgent project demand can be met from ready inventory.

Materials and how they are chosen

45# high carbon steel: high strength for standard railway joints.

50Mn alloy steel: higher toughness for heavy-duty crane tracks.

Q235B and Q345B: cost-effective options for light-duty or temporary track.

Other grades on request: stainless steel, heat-treated steel or special alloys can be produced where the operating conditions require them.

Selection and Installation Points to Check

Choose the joint by rail weight, section profile and the duty of the line, then confirm the bolt pitch and hole pattern against the drilling of the rails on site. For crane rails, the joint must match the crane rail section exactly and is often galvanized for exposed duty. For track circuits, verify the insulation resistance of the joint and the complete isolation of the fish bolts and end posts. During installation, keep the joint faces clean and unpainted at the contact surfaces, tighten the bolts evenly to the specified torque, and check gauge and level across the joint with the same tolerance applied to plain line.

Frequently Asked Questions About Rail Fishplates

Q: What is the main function of a fishplate?
It joins two rail ends so the track stays continuous, holds gauge and level across the joint, and transfers wheel loads from one rail to the next.

Q: Why is a fishplate also called a joint bar?
Both names describe the same steel bar bolted to the rail web. Fishplate is the traditional railway term and joint bar is common in North American practice.

Q: What steel is used for rail fishplates?
Common grades are 45# high carbon steel for standard track, 50Mn alloy steel for heavy-duty crane tracks, and Q235B or Q345B for light-duty and temporary lines.

Q: When is an insulated rail joint used?
It is used where the track circuit must be electrically separated, for example near power plants or on sections exposed to stray current.

Q: What is a compromise joint?
A compromise joint connects two rails of different sections or profiles, such as a switch expansion joint, and is normally manufactured to order.

Q: How many bolts does a fishplate need?
Standard joints are supplied as 4-hole or 6-hole patterns. The number and pitch follow the rail weight and the drilling of the rail being joined.