Box Wrench As the name implies, the box wrench (called a ring spanner in England) usually has a completely en- closed head, and may have six or 12 flats. A 12-flat box wrench engages the corners of the nut and can be used on both hexagonal- and square-headed bolts. A 6-flat box wrench is normally shaped to fit against all 6 sides of hexagonal nuts and it provides a very tight fit that permits considerable force to be applied. Box wrenches are stronger than open-ended wrenches, but they need access to fit it over the nut, which is not required by open-ended wrenches.   Offset Box Wrench Among the most useful box wrenches are those with offset heads which permit using them with bolts and nuts in awkward or hard-to-access places, since they provide room for your hand to move without hitting the work piece. Line or Split Box Wrench The line wrench, also called a split box wrench, is a hybrid that has a section of the box removed so the 6- or 12-point jaws can be located like an open-ended wrench. These are usually used when working on fuel or brake line fittings when it is necessary to pass over the line itself, hence the name.   Adjustable Wrenches The obvious advantage of an adjustable wrench is that it can work on a whole range of nut sizes within the capacity of its jaws. The most common version has jaws set at an angle of 15 degrees to the shaft, but other angles are also avail- able. Most professional techs are not big fans of using adjust- able wrenches, and they will usually opt for open-end or box wrenches whenever they have a choice. There are, however, those times when an adjustable wrench is the tool of choice. When using an adjustable wrench it is important to adjust the jaws so that they have a good fit on the nut. The most com- mon adjustable wrenches use a worm screw located close to the opening jaw which has a rack engaged with the screw, thus making it easy to adjust with the finger and thumb of the hand holding the wrench. A variation of the adjustable wrench rarely used in automotive work is the monkey wrench. Allen Wrenches Allen wrenches – also known as allen keys – are simple hexagonal-shaped rods with right-angle bends. They are designed to fit into the head of a bolt which has a matching hexagonal-shaped recess in the head – they are often found where space clearance is limited, such as for securing exhaust headers to an engine.
A set of high-quality combination wrenches, both SAE and metric, is essential in any Corvette garage.