The efficiency and durability of a fish-plate depends materially upon its angle of contact with the under side of the head of the rail, and the extent of its contact surface. It would be an error to suppose there is little or no wearing away in fish-plates, as in reality there is very considerable wear, and especially in rails of lighter section. If the under side of the head of rail has a curved outline, as in the rail in Fig. 287, there will be some difficulty in ensuring a perfect fit in the fish-plates; the curve of the one may not quite correspond to the curve of the other, and the contact surface will be very small. It is better to make these contact surfaces in straight lines, and to a wide angle rather than to an acute angle. In Fig. 288 the under side of head and corresponding top of fish-plates are set at an acute angle, and fish-plates to this pattern will soon wear up to the vertical web of rail, and cause a loose noisy joint. In Fig. 284, showing a different type of rail, the contact surfaces are set at a very much wider angle, and will allow much more wear before the fish-plates can work close up to the web of the rail. When once the fish-plates are close up to the web, the best and 206 tightest bolts cannot prevent the vertical play in the ends of the rails. A hammering sound will announce each successive drop of the wheels from one rail to the other, more distinctly, perhaps, at slow speeds than when travelling quickly, but existing equally under both conditions. The unpleasant jarring sensation is annoying to the passengers, and has a straining, loosening effect on all the bolts and fastenings. Unless the fish-plates have a thorough continuous bearing against the upper and lower shoulders of both the rails, it will be impossible to obtain a smooth even joint. A road may have good rails, good chairs, and good sleepers, but if the fish-plates are worn and loose the entire permanent way may be pronounced faulty, and all on account of a minor defect which can be easily remedied. With strong, properly fitting fish-plates, the position of the joints should be imperceptible when passing over them in a train. The writer has had many miles of line where the fish-plates have worn hard up to the rail web. In cases where the rails were good, with the prospect of a long life, new fish-plates of suitable section have been provided. In others, thin wrought-iron plate liners, 1/16 or 1/12 of an inch thick, have been inserted, as in Fig. 291, so as to bring the plates well out from the web, and allow the fish-bolts and fish-plates to exercise the free gripping action which is absolutely necessary to prevent the vertical rising and falling of the rail-ends during the passage of a rolling load. Fish-plate liners of the above description have given excellent results, and have restored the efficiency of the fish-plates for several years.