324 RAILWAY CONSTRUCTION. 



With a few turns of the bolt, the crab-nut is brought close up to 

 the underside of the sleeper, the spur-points become embedded in 

 the wood, and hold the nut firmly in position during subsequent 

 tightening of the bolt. Crab bolts are extensively used with 

 flange or flat-bottomed rails, and also in switch chairs and in 

 crossings. A large number of flange rails are used with one hole 

 through the flange at each end of rail, and a crab bolt passed 

 through the hole and through the sleeper next to the joint, as 

 shown in Fig. 332. This system checks the creeping of the rails 

 by effectually securing or anchoring each rail to two of the 

 sleepers. As there is always a tendency for these rails to crack 

 through to the outside at the flange-holes, it is very desirable to 

 have as few holes as possible. The two above described will be 

 found sufficient for all practical purposes. To avoid punching 

 or drilling more holes in the flanges of the rails, additional 

 or intermediate crab bolts can be used by means of the fang clips 

 shown on Fig. 333. The crab bolt is passed through the fang 

 clips and through the sleeper close up to the flange of rail, and 

 by screwing it round in the crab-nut under the sleeper the fang- 

 clip is pressed down until the two spurs are driven into the 

 timber, and the rail held securely in its place and to gauge. 

 Intermediate crab-nuts and fang-clips should always be used in 

 pairs, one on each side of the rail. Possessing more holding- 

 down power than ordinary spikes, they are particularly valuable 

 on sharp curves. 



In some cases flange rails are laid in small cast-iron saddles, 

 or chairs, as shown in Fig. 334, one end of the rail-seat having 

 a recess to prevent the rail tilting upwards and outwards. An 

 ordinary spike may be used for the inside end of chair, and a 

 crab bolt with bent washer for the other. Unless the fastenings 

 can be kept always tight, the above arrangement makes a very 

 noisy, clattering road, as there are so many metal surfaces in 

 contact, and so little to deaden the vibration. For narrow flange 

 rails carrying heavy rolling load, chairs may be necessary to 

 increase the bearing surface on the sleeper, but with rails having 

 flanges five inches wide and upwards, it is better to let the 

 flange rest direct on the wood of a properly grooved sleeper, and 

 thus obtain a smoother and less noisy road. 



On exceptionally sharp curves, wrought-iron or steel tie-bars, 

 as in Fig. 335, are sometimes used to maintain the line to gauge. 

 They may be made out of bars 3 inches wide by an inch thick, 



