A fishplate is a flat metal plate used to join two wood or metal members by means of a number of bolts or nails passing through both the member and plate. Fishplates are generally associated with train track joints although they are also commonly used to connect other materials. Fishplates impart a sturdy mechanical joint which requires little or no profile modification of the members they join. Although fishplates are typically made of metal, other materials such as plastics and composites may add additional flexibility to their range of use.
Traditionally, fishplates are used to join sections of train track and formed to fit into the inner profile of the track. They are drilled with a number of holes which are repeated on the ends of the sections to be joined. Once the two track ends have been correctly aligned, the holes in the fishplate are lined up with those in the track sections and bolts inserted and tensioned. The upper and lower edges of the fishplate are often bevelled, causing the plate to wedge itself into the track profile as it is being tensioned, and making for a more secure joint. This method of joining components such as train track sections requires no profiling and weakening of the material to complete the joint.
Fishplates are produced with a range of profiles allowing for track sections of differing heights or those used in points arrangements to be joined. When electric traction railroad tracks and those carrying separate circuits are joined, a braided cable bridge piece is typically added to ensure electrical continuity. Some fishplate designs also incorporate a lip or flange which extends below the lower edge of the rail track to facilitate attachment to the concrete or wooden ties used to support the track. This attachment is generally achieved with bolts or specially designed spikes which pass through holes in the flange.
Railroad tracks are not the only construction components which may be connected using fishplates. This type of joint is commonly used in other steel and timber structures and functions in a similar fashion to train track joints. Fishplates used to join timber may have protrusions included on their inner faces which mate into cut outs on the face of the timber component. This affords the joint good shear force resistance as well as linear and axial strength. Fishplate joints made of plastic and resin composites work well when connecting similar materials as they match the flexible nature of the joined components.