A heavy steel plate with a flat bottom and a canted top surface that sits between the rail base and the wooden tie. It distributes the immense weight of passing trains over a wider area of the wood to prevent the rail from cutting into the tie. The plate also provides holes for spikes to hold the rail at the correct gauge and inward tilt.
Heard on the job
We need to drop a bundle of tie plates at mile 42 before the spikers get there.
Insider tip
A properly seated tie plate will have a slight inward cant, usually 1 in 40, to match the taper of the train wheels.