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From adjustable to Allen, we've got everything you need to know about wrenches.
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The first nuts and bolts, which were put to use during the early years of the Renaissance, had square heads. The hexagonal (six-sided) design followed soon afterward and remains the dominant variety today, although square heads are still the rule on carriage and lag bolts.
Whatever the number of sides (called flats) on a nut or bolt head, there are several tools designed specifically to tighten or remove them. Each of the different types have significant attributes and disadvantages, but there are some dissimilarities between box-end, open-end, and combination wrenches.
Wrenches are made with openings that are slightly larger than the nuts or bolts they are designed to fit (typically, the clearance is a few thousandths of an inch). If the fit of the wrench is too loose, however, it will round off the points of the nut or bolt head.
All wrenches are available in many sizes, and can be purchased individually or in sets. A small set may have six to 10 wrenches, ranging in size from perhaps five-sixteenths to one inch. Standard wrenches are sold in sixteenth-inch increments up to one and a half inches (and in metric sizes, too, of course). The length of the tool varies in proportion to its size, ranging from about four inches to almost two feet. The logic is that the shorter (or longer) tool minimizes (or maximizes) the amount of force you can use to tighten a smaller (or larger) nut. This helps avoid shearing off bolts through the application of too much pressure.
Box-end and open-end wrenches are both sold with different-sized wrenches at either end of individual tools. This economical approach means that a five-piece set will actually contain twice that many sizes of wrench.
You'll also find that two wrenches of the same size and kind can have wildly different price tags. The explanation lies in the materials and manufacturing process. The best wrenches are made of alloys like chrome or vanadium, while less expensive tools are made from molybdenum steel or are simply stamped from sheet metal. The stamped wrenches are bulkier (more material is needed for strength), and are quite useful for occasional light duty. For frequent use, however, and for virtually any automobile applications, more expensive tools will prove the better investment.
Box-End Wrenches. These are closed-end wrenches, typically with six or 12 points around the inside diameter of the jaws. The six-pointed jaw is designed to fit hexagonal heads and nuts, while the 12-point configuration will also accommodate a square nut. The ends of the wrench are offset slightly. Box-end wrenches usually offer a firmer grip than do open-end wrenches. The thin wall of the jaw also makes access to nuts in tight spaces easier, but there are situations where these wrenches cannot be used, since they have to be slid on over the end of the bolt.
Open-End Wrenches. The flat jaws of these wrenches are slid around nuts or bolt heads and levered for loosening or tightening. The open ends allow the tool to be slid over the nut in tight quarters where there would be insufficient space for a box wrench or a socket, or where the length of a shaft or pipe interferes. Open-end wrenches are the quickest and easiest wrenches to use, but they will not always fit into tight quarters.
Combination Wrenches. Combination wrenches have an open-end jaw at one end of the tool and a box-end wrench of the same size at the other. As there are many situations where one or the other type simply won't work, combination wrenches can be handy indeed. However, if you require wrenches only infrequently, the added expense of combination wrenches may not be necessary.
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