Update time：2014-03-18 Source: WIKI
A tie plate, baseplate or sole plate is a steel plate used on rail tracks between flanged T rail and the crossties. The tie plate increases bearing area and holds the rail to correct gauge. They are fastened to wooden ties by means of spikes or bolts through holes in the plate.
The part of the plate under the rail base is tapered, setting the cant of the rail, an inward rotation from the vertical. The usual slope is one in forty ( 1.4 degrees ). The top surface of the plate has one or two shoulders that fit against the edges of the base of the rail. The double-shoulder type is currently used. Older single-shoulder types were adaptable for various rail widths, with the single shoulder positioned on the outside (field side) of the rails. Most plates are slightly wider on the field side, without which the plates tend to cut more into the outsides of the tie, reducing cant angle.
Many railways use large wood screws, also called lag screws, to fasten the tie plates (or baseplates) to the railroad ties.
Tie plates came into use around the year 1900, before which time flanged T rail was spiked directly to the ties.