220 RAILWAY CONSTRUCTION. 



The fish-bolts, Figs. 320 and 321, are of a form which is in 

 very general use both for steel bull-head rails and steel flange 

 rails. By making the neck square or pear-shaped, to fit into 

 corresponding hole in the fish-plate, the bolt is prevented from 

 turning round when the wrench or spanner is applied to tighten 

 the nut. A channel or groove is sometimes rolled on the outside 

 of fish-plate to grip bolts made with square heads. Some 

 engineers adopt two nuts, others prefer one nut of extra depth. 

 Washers are used in some cases, but are not universal. With a 

 deep rail it is preferable to place the nuts inside, so that the 

 platelayer inspecting his length can see both rows of nuts as he 

 walks along between the rails. With shallow rails the nuts 

 must be placed outside and the cup-heads inside, to give ample 

 clearance to the wheel-flanges. 



Fish-bolts are subject to very severe work. Heavy rolling 

 loads passing over the rail-joints frequently at very high 

 speeds bring into play all the gripping power of the fish-bolts 

 to maintain a firm support of the fish-plates to ends of rails, and 

 the constant action of pressure and release produces a loosening 

 or unscrewing motion in the bolts which is very difficult to 

 counteract. Loose fish-bolts cause clattering joints and uneven 

 road, and unless promptly remedied, the screw threads are soon 

 destroyed and bolts rendered useless. Many devices have been 

 invented to prevent or check this loosening of the bolts ; one of 

 the methods, and a very simple one, consists of a plain steel bolt 

 with a steel lock-nut, made as shown in Fig. 322. As will be 

 seen from the section, one-half of the nut is tapped of the same 

 size as the bolt, and the remainder with deep-locking threads. 

 The first half of the nut is readily screwed on to the bolt, but 

 considerable force must be exerted to screw on the portion 

 having the deep-locking threads ; practically the second half of 

 the nut has to cut a new or deeper thread for its&lf when screw- 

 ing round the bolt. 



The slits or grooves at the angles of the nuts form four 

 distinct cutting edges for shaping the deep threads. As the 

 upper part of the lock-nut is divided by the grooves into four 

 separate or detached segments, these segments will be forced 

 slightly open or outwards during the action of cutting the deep 

 thread on the bolt, and from their natural tendency to return to 

 their original position they must exercise a strong gripping 

 power on the bolt This combined operation of cutting the deep 



