Rail Joint Types Explained: Common, Compromise, Joggled and Insulated Fishplates

The Job a Rail Joint Has to Do

A rail joint, also called a fishplate or joint bar, connects two rail ends and holds them in line and level so that a wheel can run from one rail to the next without a step. It carries the wheel load across the gap between the two rail ends, stops the ends spreading apart, and keeps the track continuous in both the horizontal and the vertical plane. On a poor joint the wheel impact is concentrated, which is why joint quality has a direct effect on ride steadiness, rail end batter and the life of the sleepers underneath.

Joint bars are used on light rail and heavy rail alike, and the correct bar is matched to the rail section, the hole pattern and the duty of the track.

Common Rail Joints

The common rail joint is the standard bar used for connecting rail ends of the same section. It is a straightforward rolled or forged bar, normally supplied in a 4-hole or a 6-hole version. The 6-hole bar gives a longer grip and lower bolt-hole stress and is preferred on heavier sections, while the 4-hole bar is still widely used on light and medium rail. Joint bars are supplied as a pair, one for each side of the rail, together with the bolts, nuts and spring washers.

Compromise Joint Bars

A compromise joint bar joins two rails of different sections or different heights, and is shaped so that each half matches one of the rails exactly while the running surface stays flat and smooth. Because the bar has to bridge two different profiles, it is made as two distinct parts: the gauge side bar, which controls line and gauge, and the outside bar, which carries the vertical load.

Type	Material	Unit weight	Remark
136RE-115RE	55# carbon steel	27.5 kg/pc	4 pcs per set
136RE-132RE	55# carbon steel	26.7 kg/pc	2 pcs per set
141RE-136RE	55# carbon steel	26.7 kg/pc	2 pcs per set
141RE-132RE	55# carbon steel	26.7 kg/pc	2 pcs per set
100-8 with 1/8 in vertical offset	55# carbon steel	15.6 kg/pc	2 pcs per set
100-8 with 3/8 in vertical offset	55# carbon steel	15.6 kg/pc	2 pcs per set
UIC60-P50	55# carbon steel	23.0 kg/pc	2 pcs per set
BS80A-115RE	55# carbon steel	20.0 kg/pc	2 pcs per set
UIC60 thermit welded joint	55# carbon steel	18.0 kg/pc	2 pcs per set

Bar length and material can be made to order where a rail section is not covered by the standard range. The vertical offsets shown above are used where two rails of different height must meet with the running surfaces aligned.

Joggled and Bulge Rail Joints

A joggled rail joint, also called a bulge rail joint, has a pronounced bulge in the middle of the bar. The bulge is placed where the rail ends meet so that the bar bridges a gap in a broken or cracked welded rail. Because it can be fitted quickly and works on a range of rail sections, the joggled bar is normally kept as an emergency clamp for temporary repair of welded rail until a permanent weld can be made. It is not intended for permanent service.

Insulated Rail Joints

An insulated rail joint separates the two rail ends electrically so that track circuit current cannot pass through the joint. This is essential where the track is divided into signalling sections, and also at the boundary of an electrified area. The insulation is created by an end post between the rail ends plus insulating sleeves and washers at the bolts, with the joint bar itself isolated from the rails.

Glued insulated rail joint: the bars are bonded to the rail ends with adhesive and the assembly is cured before installation, giving a stiff, long-lasting joint with few components.

Inserted end post: a solid insulating post is inserted between the rail ends during assembly, used where the joint has to be built up in track.

Glued end post: the end post is bonded into the joint, which improves water resistance and electrical reliability in wet or contaminated locations.

Glued insulated joints are the usual choice in long welded rail and in track-circuited areas, because they hold their insulation resistance for longer and need less maintenance than a simple bolted joint with insulating plates.

What Fishplates Do for the Track

Join rails: connect two separate rail sections into a continuous running surface.

Maintain alignment: hold rail ends in correct line and level so the ride stays smooth.

Transfer load: distribute the wheel load from one rail end into the next.

Prevent separation: stop the rail ends spreading apart, which would allow wheels to drop and derail.

Provide stability: add stiffness and continuity at the weakest point of the track structure.

Frequently Asked Questions

Q: What is the difference between a rail joint and a fishplate?
They are the same component. Fishplate is the traditional British term and rail joint or joint bar is the more general one; all describe the bar that connects two rail ends.

Q: When should a 6-hole joint be used instead of a 4-hole joint?
A 6-hole bar is used on heavier rail and on higher-duty track because the longer grip lowers bolt-hole stress and reduces rail end movement, while 4-hole bars remain common on light rail.

Q: What is a compromise joint bar for?
It joins two rails of different sections or heights, with a gauge side bar to control line and gauge and an outside bar to carry load.

Q: Why are insulated rail joints needed?
They block track circuit current at the boundaries between signalling sections and at the limits of electrified territory, while still carrying the wheel load.

Q: Can a joggled rail joint be left in track permanently?
No. The joggled or bulge joint is an emergency clamp for broken or cracked welded rail; it is a temporary repair until a proper weld or permanent joint is installed.

Q: What material are joint bars made from?
The compromise bars listed above are produced in 55# carbon steel, and the bar length and material can be made to order for non-standard rail sections.