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What Is a Rail Fishplate and Why Does It Matter?
So what exactly is a fishplate?
A fishplate, sometimes called a joint bar, splice bar, or rail joint bar, is a flat steel plate that sits against the web of the rail and is bolted through both the plate and the rail end to hold two rail lengths together. They always come in pairs, one on each side of the rail, clamping the joint from both sides simultaneously.
The name is a bit unusual. It comes from "fish," a wooden piece historically used to reinforce a ship's mast by splinting it on both sides. The same idea was applied to rails in the 1840s, when William Bridges Adams developed the fishplate to replace the earlier scarf joint system, which required the rail to be thinned at its ends, precisely where the stress was greatest. A fishplate sits alongside the rail rather than weakening it, and the concept has not changed much since.
Look at a section of older jointed track in Australia and you will see fishplates at every joint, every 13 metres or so. Each joint has two fishplates, one on the field side and one on the gauge side of the rail, held by four or six fish bolts per pair depending on the specification.
How does a fishplate work?
The fishplate works through clamping. The inner faces of the plate are tapered inward on both the top and bottom surfaces so that as the fish bolts are tightened, the plate is drawn in against the rail web and the tapered faces wedge against the underside of the rail head above and the top of the rail foot below. This creates a clamped joint that resists both vertical and lateral movement.
The goal is a continuous running surface. When a train wheel rolls across a rail joint, it should not feel a significant dip, step, or gap. A well-maintained fishplated joint with the correct bolt torque and no worn components achieves this reasonably well. A worn, loose, or cracked joint is a different story, which is why fishplate and fish bolt maintenance is a regular inspection item on any section of jointed track.
On electrified networks, the fishplate also matters electrically. Rail carries traction return current in addition to structural loads, and fishplates in reasonable condition provide electrical continuity across the joint. Where that continuity is unreliable, supplementary bonding wire is installed across the joint to maintain the circuit. Browse track components and fasteners including fish bolts available through Rail Depot Direct.
The different types of fishplates used in Australian rail
Not all fishplates are the same. The specific type used depends on the rail profile, the function of the joint, and the signalling environment of the section.
1. Standard fishplates
Standard fishplates are the most common type. They are made from medium or high-carbon steel, machined to match the specific rail profile they are used with, and drilled with four or six holes for the fish bolts. In Australia, the hole pattern and plate dimensions are matched to the Australian Standard rail profiles in service on that section, including AS 41kg, AS 47kg, AS 53kg, and AS 60kg profiles. You cannot simply use a fishplate from one rail profile on a different profile and expect it to fit correctly.
2. Insulated fishplates
On sections of track where signalling systems use the rail as part of an electrical circuit, the joint between two track circuit sections needs to be electrically isolated. An insulated fishplate achieves this by using a non-conductive material, either a composite or an insulated metal assembly, to create a physical joint that maintains structural continuity while breaking the electrical circuit.
Insulated joints are one of the most maintenance-intensive joint types in Australian rail signalling. The insulating material can deteriorate under traffic loading, and a failed insulated joint can cause signal failures that affect train operations across a section of network. Track geometry inspection of insulated joint areas is typically more frequent than standard joint inspection.
3. Compromise fishplates
When two different rail profiles meet at a joint, standard fishplates will not fit both rails correctly because the web heights and foot widths are different. A compromise fishplate bridges the step between the two profiles, with one face machined to fit the first rail profile and the other machined to fit the second. These are common at transitions between track sections of different specification, for example where an older lighter-profile branch line joins a heavier-profile main line.
Fishplates in the context of Australian track
| Joint type | Where you typically see it | Key maintenance consideration |
|---|---|---|
| Standard bolted joint | Older regional and freight lines, yards and sidings, heritage railways | Regular bolt torque checks, rail end wear inspection, crack monitoring |
| Insulated joint | Track circuit boundaries on signalled lines | Insulation condition monitoring, more frequent inspection than standard joints |
| Compromise joint | Profile transition points between sections of different rail specification | Profile alignment inspection, bolt torque maintenance |
| Emergency joint | Temporary repair of a broken or damaged rail pending full replacement | Short-term fix only, requires monitoring and planned replacement |
| Glued insulated joint | Modern insulated joint type using adhesive bonding for higher strength | Lower maintenance frequency but requires specialist inspection and repair |
Why fishplate condition matters
Here is the honest version of why you should care about fishplate maintenance.
A rail joint is structurally the weakest point in a section of jointed track. Every time a train wheel rolls over it, the joint experiences an impact load that is higher than the load on the continuous rail either side. Over time, this impact loading causes the fish bolt holes in the rail to elongate, the bolts themselves to work loose, and the rail ends to pump up and down slightly with each passing axle. If that movement is not controlled by tight, well-maintained bolts and undamaged fishplates, the movement accelerates and the joint deteriorates faster.
The failure modes range from annoying to dangerous. At the annoying end, a loose joint creates a noticeable rough ride and an audible impact that worsens over time. At the dangerous end, a cracked fishplate that is not detected during inspection can fracture under load, removing the structural support from the joint. A cracked rail end at an unmaintained joint can extend into a full rail break. Both of these are serious safety events.
This is exactly why track inspection regimes in Australia include specific attention to joint condition, and why fish bolt torque is a standard check item on any section of jointed track.
Fishplates versus continuous welded rail
If fishplates are the weak point in jointed track, the obvious question is why not eliminate them altogether. And on most major Australian networks, that is exactly what has happened.
Continuous welded rail (CWR) joins individual rail lengths by welding rather than bolting, eliminating the joint entirely. No joint means no impact load, no bolt maintenance, no rail end wear, and a much smoother ride. On the ARTC interstate network and the metropolitan networks in Sydney, Melbourne, and Brisbane, CWR is the standard.
But fishplates have not disappeared entirely. They are still used at the boundaries of CWR sections where the continuously welded rail terminates, at insulated joints for signalling circuits that cannot practically be replaced with glued joints, at emergency repairs where a temporary joint needs to be made quickly in a possession, and on regional and freight lines where the traffic levels do not justify the capital cost of converting to CWR.
Any maintenance team working across Australian rail networks will encounter fishplated joints regularly, and knowing how to inspect them, what to look for, and when to escalate is a core part of track maintenance competency.
What to check during a fishplate inspection
When you are checking a fishplated joint during a patrol or inspection visit, these are the things worth looking at closely:
- Fish bolt condition and torque: Bolts should be tight and show no signs of rotation or significant corrosion. A bolt that spins freely is not providing clamping force.
- Fishplate cracks: Look along the length of the plate for visible cracks, particularly around the bolt holes where stress concentration is highest.
- Rail end condition: The rail ends at a joint experience higher wear than the running rail either side. Check for rail end batter (deformation of the rail end from repeated impact), shelling, or cracking.
- Gap at the joint: On jointed track, a small gap between rail ends accommodates thermal expansion. A gap that has closed completely on a warm day indicates compressive stress that could cause buckling. A gap that has opened significantly on a cold day indicates tensile stress and risk of joint separation.
- Joint geometry: Check that the running surfaces of the two rails are flush. A step at the joint, even a small one, creates an impact load every time a wheel passes over it.
Browse track measuring and inspection equipment including straight edges and gauges for joint inspection through Rail Depot Direct.
Frequently Asked Questions
What is a fishplate made of?
Standard fishplates are made from medium to high-carbon steel, heat treated for strength and wear resistance. Insulated fishplates use non-conductive composite materials or a metal plate with insulating inserts and end posts to isolate the electrical circuit while maintaining structural strength.
How many fish bolts does a fishplate use?
Either four or six bolts per pair of fishplates, depending on the rail profile and the load conditions. Six-bolt joints are used where higher load distribution is needed, such as on heavier-duty freight lines and at higher-stress locations.
Can you use a fishplate from one rail profile on a different one?
No. Fishplates are machined to match the specific web height, foot width, and taper of the rail profile they are designed for. Using the wrong profile fishplate produces poor contact geometry and uneven clamping force.
Why are some fishplates a different colour or material?
Insulated fishplates are often made from composite materials or have coloured end posts to identify them visually as insulated joints. The identification matters because the maintenance requirements and failure modes of insulated joints are different from standard bolted joints.
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