OPEN-END WRENCHES

The size of any wrench used on bolt heads or nuts is determined by the size of the opening between the jaws of the wrench. The opening of a wrench is manufactured slightly larger than the bolt head or nut that it is designed to fit. Hex-nuts (six-sided) and other types of nut or bolt heads are measured across opposite flats (fig. 1-26). A wrench that is designed to fit a 3/8-inch nut or bolt usually has a clearance of from 5 to 8 thousandths of an inch. This clearance allows the wrench to slide on and off the nut or bolt with a minimum of "play." If the wrench is too large, the points of the nut or bolt head will be rounded and destroyed. There are many types of wrenches. Each type is designed for a specific use. Let's discuss some of them. OPEN-END WRENCHES Solid, nonadjustable wrenches with openings in one or both ends are called open-end wrenches. (See fig. 1-26.) Usually they come in sets of from 6 to 10 wrenches, with sizes ranging from 5/16 to 1 inch. Wrenches with small openings are usually shorter than wrenches with large openings. This proportions the lever advantage of the wrench to the bolt or stud and helps prevent wrench breakage or damage to the bolt or stud. One exception exists. Hydraulic piping installations for catapult and arresting gear are often in close spaces. During certain phases of hydraulic maintenance it may be impossible to swing an ordinary wrench because of its length. Ordinary wrenches that are normally available increase in length as their size increases. Thus, when a large-size wrench is needed, the length of the wrench sometimes prevents its use, due to the space available to swing the wrench. The Bonney wrench, shown in figure 1-27, is an open-end wrench that may be used to great advantage because of its thickness and short length. This wrench is normally procured in the larger sizes, although it is available in a range of sizes to fit most hydraulic fittings. Open-end wrenches may have their jaws parallel to the handle or at angles anywhere up to 90 degrees. The average angle is 15 degrees (fig. 1-26). This angular displacement variation permits selection of a wrench suited for places where there is room to make only a part of a complete turn of a nut or bolt. If the wrench is turned over after the first swing, it will fit on the same flats and turn the nut farther. After two swings on the wrench, the nut is turned far enough so that a new set of flats are in position for the wrench, as shown in figure 1-28. Handles are usually straight, but may be curved. Those with curved handles are called S-wrenches. Other open-end wrenches may have offset handles. This allows the head to reach nut or bolt heads that are sunk below the surface. 1-19 Figure 1-26.—Open-end wrenches. Figure 1-27.—Bonney wrenches.