Engineer's Square
An Engineers Square is similar to the Try Square except it is smaller and made of metal. It is used to check that the edges of the plastic or metal are square or to scribe lines at Right Angles to an edge. The engineer’s square has to conform to the British Standard BS939, which means that all surfaces are accurate and not just the inside angle like a Try square.
Engineer's squares also have a groove or relief where the inner edge of the blade meets the inner face of the stock. The groove prevents swarf, dirt, or grit getting in-between the engineer's square and the workpiece, reducing the risk of inaccuracy when checking the workpiece is square.