SPANNER WRENCHES

movable jaw on a pipe wrench is pivoted to permit a gripping action on the work. This tool must be used with discretion, as the jaws are serrated and always make marks on the work unless adequate precautions are observed. The jaws should be adjusted so the bite on the work will be taken at about the center of the jaws. Strap Wrench The strap wrench (fig. 1-39) is used for turning pipe or cylinders where you do not want to mar the surface of the work. To use this wrench, the webbed strap is placed around the pipe and passed through the slot in the metal body of the wrench. The strap is then pulled up tight; and as the mechanic turns the wrench in the desired direction, the webbed strap tightens further around the pipe. This gripping action causes the pipe to turn. SPANNER WRENCHES Many special nuts are made with notches cut into their outer edge. For these nuts a hook spanner (fig. 1-40) is required. This wrench has a curved arm with a lug or hook on the end. This lug fits into one of the notches of the nut, and the handle is turned to loosen or tighten the nut. This spanner may be made for just one particular size of notched nut, or it may have a hinged arm to adjust it to a range of sizes. Another type of spanner is the pin spanner. Pin spanners have a pin in place of a hook. This pin fits into a hole in the outer part of the nut. Face pin spanners are designed so that the pins fit into holes in the face of the nut (fig. 1-40). When you use a spanner wrench, you must make sure the pins, lugs, or hooks make firm contact with the nut while the turning force is transferred from the wrench to the nut. If this is not done, damage will result to tools or equipment or injury to personnel. SETSCREW WRENCHES (ALLEN AND BRISTOL) In some places it is desirable to use recessed heads on setscrews and capscrews. One type of screw (Allen) is used extensively on office machines and in machine shops. The other type (Bristol) is used infrequently. Recessed-head screws usually have a hex-shaped (six-sided) recess. To remove or tighten this type of screw requires a special wrench that will fit in the recess. This wrench is called an Allen-type wrench. Allen wrenches are made from hexagonal L-shaped 1-26 Figure 1-39.—Strap wrench. Figure 1-40.—General-purpose spanner wrenches.