Try Square
From DT Online
A Try Square is an ‘L’-shaped tool used for testing the Squareness of material and for marking lines at right-angles to an edge or surface.
A traditional Carpenter's Try Square has a blade of tempered steel which is fixed at right-angles to a wooden stock with rivets passing through brass plates on each side of the stock. The stock was made of Rosewood or Ebony and the brass plates are to prevent the wood from splitting to ensure the blade is held securely. The inside edge of the wooden stock is faced with brass to prevent the stock from wearing.
Modern versions may be made with stocks moulded in plastics composites or die cast in aluminium.
An Engineer's Try Square is the metalworker's equivalent. It has a metal blade pinned or welded to a steel stock which is notched at the inside corner to prevent small burrs or particles affecting its accuracy in use.