fishplate

A fishplate is a steel bar, typically 12 to 24 inches long and 4 to 6 inches wide, bolted across the joint between two abutting rail ends to splice them into a continuous track. The name comes from its shape: wider in the middle and tapered at the ends, resembling a fish. Each fishplate is drilled with four to six holes that align with corresponding holes in the rail webs on both sides of the joint, and high-strength bolts are drawn through with lock washers to create a rigid connection.

Fishplates come in two primary types: standard plates for main-line track, which must handle full tonnage and dynamic loading, and compromise plates used on sidings or yards where lower stresses apply. Standard plates for heavy rail (typically 115 to 136 pound rail) are made from medium-carbon steel, heat-treated to around 140 ksi tensile strength. The plates must be matched precisely to the rail section; a 115-pound rail requires different fishplates than a 130-pound rail, and they cannot be substituted without risking joint failure.

Common failures and maintenance

Fishplate joints are stress concentrations where rail fatigue cracks often initiate, particularly at the bolt holes. Bolts loosen under the combined effects of vibration, thermal cycling, and the lateral forces of curve negotiation. On high-traffic lines, fishplate bolts require regular retensioning during track inspections, typically every six months to two years depending on traffic volume and speed. A loose fishplate produces a distinctive clunk when wheel flanges strike it, audible from a distance on quiet track.

The fishplate has largely given way to welded rail on main lines, where continuous welded rail (CWR) eliminates the joint entirely and reduces maintenance. However, fishplates remain the standard on branch lines, sidings, yards, and many legacy installations where the cost of rail replacement or welding equipment is not justified. They are also used as temporary solutions during track maintenance and at rail terminal points where expansion is deliberately accommodated.

Correct installation requires that fishplate bolts be torqued to specification (typically 150 to 200 foot-pounds depending on bolt diameter and grade) and that the rail ends mate cleanly with minimal gap. A bent or cracked fishplate, or one with stripped bolt holes, must be replaced as a set; attempting to drill new holes or re-weld a damaged plate compounds the structural weakness and is not accepted practice in Class 1 railroad maintenance standards.