Why Are Rail Joiners Called Fish Plates?

Rail joiners are called fish plates because early designs had a tapered, curved profile that resembled the body or tail fin of a fish. The name was carried over from shipbuilding, where similar pieces of timber or iron were used to strengthen masts, and it stuck as the joiner became a standard part of every bolted track.

Where the Name Comes From

Visual similarity: early plates, especially those made for fish-bellied cast iron rails or used to reinforce ship masts, taper at the ends and look like a fish.

Shipbuilding: the term comes from fish pieces, the strips used to strengthen a wooden mast. The same idea was adapted to rail joints.

Linguistic root: the name may also derive from the French word ficher, meaning to fix or fasten, which matches the job the plate does.

Whichever explanation is preferred, the working meaning is the same: a fish plate, also called a rail joiner or joint bar, is the bar that bolts two rail ends together and carries the bending moment across the gap.

How Fish Plates Are Classified

Fish plates are grouped by the shape of the bar and by the type of joint they serve:

Standard fish plates: a flat bar with bolt holes on both sides, shaped for the straight joint of a standard rail section. This is by far the most common type and covers most weight-classified rail sizes.

Special-shaped fish plates: the profile follows the specific angle of a joint, for example on curved track, or the geometry of a non-standard rail section. They keep the running surface smooth where a standard bar could not seat correctly.

Typical Joint Bar Specifications

Weights are nominal per piece and should be confirmed against the mill or forging certificate, since hole pattern and bar length change the finished weight of a joint bar.

Materials, Holes and Finishes

Materials: carbon steel grades such as 45# and 50# are used for the common rolled bars, while Q345 is used for forged bars on the heavier UIC sections. Grade and mechanical properties should be stated on the drawing.

Hole pattern: bars can be supplied semi-finished without holes or finished with holes drilled and chamfered. Both 4-hole and 6-hole bars are produced, with round or oval holes depending on the fish bolt used.

Finishes: plain, hot-dip galvanized, or sandblasted and oiled for forged bars. Galvanizing is usual on exposed crane rail joints and wet locations.

Tooling: a wide range of joint bar moulds and dies is held, including bars intended for welded joint applications, which allows matching most rail sections without new tooling.

Where a bolted joint is not wanted at all, an aluminothermic welded joint can replace it, but fishplated joints remain essential at insulated joints, at temporary closures and wherever a track may need to be opened again quickly.

Frequently Asked Questions

Q: Are fish plates and joint bars the same thing?
Yes. Fish plate, rail joiner and joint bar describe the same component. Regional usage varies, but all three names refer to the bar that bolts two rail ends together.

Q: Why is the fish plate tapered?
The tapered profile follows the bending stress distribution along the joint and matches the rail web geometry, so the bar seats on the rail sides without fouling the head or foot.

Q: How many bolt holes does a joint bar have?
Both 4-hole and 6-hole versions are produced, with round or oval holes. The correct pattern is decided by the rail section and the fish bolt diameter specified for the track.

Q: Can joint bars be supplied without holes?
Yes. Semi-finished bars without holes are supplied so that drilling can be carried out locally or in the workshop to match an existing rail.

Q: What material is used for a forged joint bar?
Forged bars for the heavier UIC sections are commonly made from Q345 steel, while rolled bars for 43 kg/m and 50 kg/m rails use 45# or 50# carbon steel.

Q: How are crane rail joints protected?
Joint bars for crane rails such as CR135 and CR171 are supplied plain or hot-dip galvanized, and forged bars are sandblasted and oiled to limit corrosion before installation.