A Tommy bar, also called a t-bar or wrench lever, is a short bar or rod that is inserted through the shaft of another tool, most commonly a socket spanner or box spanner, to provide extra leverage when turning the tool. Spanners are used to tighten or loosen nuts and bolts. A spanner used with a Tommy bar has a hole through the shaft where a bar is inserted to help turn the nuts and bolts, for example when changing car tires, removing hubcaps, or doing adjustments to a motorcycle tire. Tommy bar tools come in many different sizes with varying diameters and of varying lengths, and are usually made of aluminum, steel or stainless steel that can be chrome-plated, zinc-plated or powder-coated. A Tommy bar tool is commonly included in tool kits provided with a car or motorcycle.
The type of spanner most commonly used with a Tommy bar is the box spanner, also called a box wrench. This tool is a hollow tube with a socket at each end, and the t-bar is inserted through the two holes in the hollow tube to help turn the spanner. T-bars can also be used with jackscrews.
There are different types of Tommy bars. Some come with a ball-locking device that prevents the rod from sliding out while it is being used. Other t-bars, for example many of those used as car tools, have a bent tip for this same reason. There are also stepped Tommy bars that are made up of several sections of varying diameters, making it possible to insert the t-bar in spanners with different sized holes. Very small Tommy bars are used for so-called t-bar screws that have a t-bar inserted through a hole in the screw's head in order to turn it more easily. These kinds of screws can be used for different purposes, for example in microphone stands and boom arms.
The diameter of the Tommy bar needed for a particular job depends on the size of the holes through the spanner being used, and the length needed is dependent on how much leverage or torque is required. It is not known exactly how the Tommy bar got its name. Some think the term originated with its use by British soldiers, sometimes referred to as "Tommys," in the first and second world wars, when Tommy bars and spanners were used to unscrew the base of bombs when disarming them.