Fig. 358.
Tap Wrench.—Wrenches for rotating a tap are divided into two principal classes, single and double wrenches. The former has the hole which receives the squared end of the tap in the middle of its length, as shown in [Fig. 358] at e, there being a handle on each side to turn it by.
Fig. 359.
The single wrench has its hole at one end, as shown in [Fig. 359] at d, and is employed for tapping holes in locations where the double wrench could not be got in.
Fig. 360.
In some cases double tap wrenches are made with two or three sizes of square holes to serve as many different sizes of taps, but this is objectionable, because unless the handles of the wrench extend equally on each side of the tap, the overhanging weight on one side of the tap exerts an influence to pull the tap over to one side and tap the hole out of straight. For taps that have square heads the wrench should be a close but an easy fit to the tap head, otherwise the square corners of the tap become rounded. For the smaller sizes of taps, adjustable wrenches, such as shown in [Fig. 360], are sometimes employed. These contain two dies; the upper one, which meets the threaded end of c, being a sliding fit, and the joint faces being formed as shown at a, b. By rotating the handle c its end leaves the upper die, which may be opened out, leaving the square hole between the dies large enough to admit the squared tap end. After the wrench is placed on the tap, c is rotated so as to close the dies upon the tap.