The History and Evolution of Rail Fishplates

In the early days of railway development, two steel plates bolted together were installed on either side of a rail joint to connect the rail ends. This component is known as a “fish plate” in the United Kingdom and a “joint bar” in the United States.Many people ask:Why is it called a “fish plate”? Does it really have anything to do with fish?To understand this name, we need to start with an early form of rail known as the “fish-belly rail.”

1. What is a fish-belly rail?

In the early 19th century, when railways were just emerging, steel was expensive. Engineers sought to increase material at the center—where stress was greatest—and reduce it at the ends, where stress was lower. This led to a rail profile that was “thick in the middle and thin at the ends,” resembling a fish’s belly, hence the name “fish-belly rail.”

. This type of rail was common on early British railways, such as pioneering lines like the Liverpool and Manchester Railway. Fish-belly rails were typically made of cast iron and installed on stone sleepers or chair-type supports, resulting in a non-continuous structure.

2. Problems with Early Track Joints

At that time, track joints were simply butted together and relied on support from below.

As a result, a distinct “clang” was heard as the wheels passed over them, and the joints became the most vulnerable part of the track, requiring frequent maintenance. Engineers quickly realized that the joints needed to be reinforced.

3. The True Origin of “Fish”

Although the name “fish-belly rail” contains the word “fish,” the “fish” in “fish plate” is generally believed to derive from the engineering verb “to fish”—meaning to reinforce a structure with additional plates. This term was already in use in bridge and timber construction before the advent of railways. Authoritative dictionaries, such as the Oxford English Dictionary, favor this explanation over the theory that it derives from the French word fissure (crack). In other words, a fish plate is essentially a “reinforcing plate.” However, the existence of the fish-belly rail has made the term “fish” more readily accepted in a railway context, resulting in a historical overlap of meanings between the two concepts of “fish.”

4. The Invention of the Fishplate

In the mid-19th century, with the widespread adoption of rolled rails, engineers began attaching steel plates to both ends of the rails and securing them with bolts.

British engineer William Bridges Adams promoted an improved fishplate joint design in the 1840s.

The function of the fishplate is straightforward: it clamps the two rails together, distributes wheel loads, reduces joint impact, and extends the life of the track. This represents a classic example of incremental engineering improvement.

5. How has the fishplate design evolved?

Early fishplates: These were simple flat plates with few holes. They were later gradually improved to feature a profile that conforms to the rail web, a 4- or 6-hole configuration with slightly asymmetrical hole placement, and a thicker joint area. These improvements all centered on a single core objective: to make the joint as “close to continuous” as possible.

6. From Fishplates to Continuously Welded Rails

Although fishplates significantly improved joint performance, they still suffered from issues such as changes in stiffness, noise,

bolt loosening, and fatigue cracks. After welding technology matured in the 20th century, continuously welded rails (CWR) gradually replaced mechanically joined rails. On modern high-speed railways, conventional fishplates have almost disappeared.However, they are still used for: temporary rail connections, construction transitions/ insulated joints / certain bridge sections.

7. An Interesting Historical Coincidence

In the history of railways, two terms coexist: “fish-belly rail”—so named because of its resemblance to a fish’s belly—and “fish plate”—so named because “to fish” implies reinforcement. Though they do not share the same origin, they existed side by side during the same era. This makes the use of “fish” in railway terminology seem particularly natural.

8. Conclusion

A fish plate is more than just a piece of steel; it represents a phase in the development of railway engineering:

from cast-iron fish-belly rails to the reinforcement of rail joints, and finally to continuously welded rails. It bears witness to the evolution of railways from the “jointed era” to the “continuous era.” Behind this small term lies a microcosm of the entire history of engineering.