The nuts shown in Figs. 129 and 130 have grooves cut across their

upper faces, one of these grooves being opposite a hole in the point of the bolt through which passes a pin or cotter.

The nut shown in Fig. 131 is cut half way through, and after the nut is screwed up the semi-detached portion is sprung closer to the other by a screw, which has the effect of tightening the screw of the nut on that of the bolt.

In Fig. 132 the nut shown has a plate bolted to one of its faces, this plate having a tail-pin which fits into a corresponding hole in the piece supporting the nut.

98. Various Forms of Bolts.-A stud or stud-bolt is one which is screwed at both ends, one end being screwed into one of the pieces to be connected, while the other end carries an ordinary nut. Fig. 133 shows a plain stud. Fig. 134 shows a stud with a collar, which may be circular or square. This collar serves as a shoulder, against which the stud may be screwed up tight. The collar, if square, is also useful for receiving a spanner to screw up the stud. In Fig. 135 the stud has a

If

square neck to receive a spanner for screwing it in. This figure also shows a method of locking the stud so that it cannot slacken back. the stud is required to go to the bottom of the hole, it is sometimes desirable to cut a spiral groove on it as shown in Fig. 133, so as to allow the air and any water or oil which may be in the hole to escape. This groove may be made with the edge of a file.

A tap-bolt is a bolt with a head. and is screwed into one of the pieces

to be connected while the head presses on the other piece as shown in Fig. 136.

Tap and stud bolts combined are shown in Figs. 137 and 138. Bolts

having nuts at each end are shown in Figs. 139. 140, and 141. Fig. 142 shows bolts or screws with heads slotted to receive a screwdriver.

99. Set-Screws.-A set-screw is a screw or bolt which presses on a piece so as to prevent the rotation or sliding of that piece. Examples

O

FIG. 143.

FIG. 144.

FIG. 145.

FIG. 146. FIG. 147. of set-screws are shown in Figs. 143 to 147. In Fig. 143 the set-screw is shown with a sharp, conical point, which enables it to penetrate into

the piece which it is required to set or lock. A good holding form of point is that shown in Fig. 146. In cases where the damaging action of the point of the set-screw would be objectionable, a metal pad may be used, as shown in Figs. 144 and 145. It is a good practice to let the point of the set-screw press on the bottom of a shallow groove in the piece to be locked, in cases where the piece is not locked permanently in one position, as in the locking arrangements for a nut shown in Fig. 122, and in the cotters for connecting rod ends. By this artifice the bur raised by the point of the set-screw does not interefere with the rotation or sliding of the piece when the latter has to be shifted. Set-screws are generally made of steel, and their points should be hardened.

100. Backlash in Screws-Divided Nuts.-The amount of rotary motion which can be given to a nut without causing any movement of the screw on which it works is called backlash, and is due either to imperfection in the manufacture or to wear. Backlash may be overcome by using a divided nut. For a square-threaded screw the nut should be divided at right angles to its axis; but for a triangular-threaded screw

the nut may be divided at right angles to the axis, or in a plane containing the axis. In each case the two halves of the nut are held together by bolts and nuts. In the design shown in Figs. 148 and 149, the two halves of the divided nut are provided with flanges which are bolted firmly together. The backlash is taken up by rotating one half of the nut on the other previous to tightening up the bolts. To permit of this rotation the bolt-holes are in the form of slots, as shown in Fig. 148.

CHAPTER V.

KEYS.

101. Keys.-Keys are wedges, generally rectangular in cross section, which are used for securing wheels, pulleys, cranks, etc., to shafts. Steel is the best material for ordinary keys, but wrought-iron is often used instead.

102. Saddle-Key.-The hollow or saddle key is shown in Figs. 150, 151, and 152. The first of these figures is an enlarged section of the key, while the others show it in position, securing a wheel or pulley to

FIG. 150.

FIG. 151.

FIG. 152.

a shaft. With this form of key it is not necessary to cut the shaft in any way, but its holding power is small, and it is therefore only used for light work.

103. Flat Key.-The flat key receives its name from the fact that it rests on a flat, which is formed on the shaft to receive it. Fig. 153

FIG. 153.

FIG. 154.

FIG. 155.

is an enlarged cross section of a flat key, while Figs. 154 and 155 show it in position. The holding power of this key is much greater than that of the saddle-key.

104. Sunk Key.—The sunk key is a very secure form of key, and is