An adjustable square is a tool used in construction and carpentry to determine if a component is perfectly square. Often including a bubble level into the adjustable square tool, the device can be used to determine if a board or other object is not only square, but level as well. Commonly manufactured with a steel straight edge attached to a wooden or plastic handle featuring a bolt and wing-nut, the adjustable square is manipulated by the carpenter by loosening the wing-nut, moving the steel straight edge to the desired length and re-tightening the wing-nut. This now gives the carpenter an exact reading of the squareness of the object in question.
Generally small enough to fit into a carpenter's tool belt, the adjustable square is a multiple-use tool capable of many tasks. While generally used to mark a cut line on a piece of material, the adjustable square can also aid in the installation of a door or window. By reading the bubble level in the square's handle, the carpenter is able to determine the exact placement of a door or window casing to ensure the unit is level. This makes certain that the door or window will open and close without binding or sticking once it is finished and installed.
The use of the adjustable square is also helpful in measuring concrete and brick grades as well as eaves trough drop by monitoring the position of the bubble in the level. If improperly installed, an eaves trough will not drain the rainwater, but will instead pool the water and could even collect insect larvae. When attempting to build a cement wall or brick wall on a particular grade, the adjustable square is a valuable tool that allows the mason to check the position of the level bubble, which matches the grade, periodically and ensure the work is correct. One of the most common uses of the square is assigned to cutting boards to length on a construction site. By marking the cut line with the square, the boards are properly fitted together when nailed into position.
Another handy use for the adjustable square is to determine the depth of a particular space. By loosening the wing-nut, the square can be placed over the depression or hole and the blade slid into the space until it bottoms out by making contact with another surface. The wing-nut can then be tightened and the square is removed from the hole. By measuring the distance from the tip of the adjustable square blade to the face of the handle, an accurate measurement can be found to allow a board cut to fit the space to fit perfectly.