These cabinetmaker's squares are used to lay out or transfer measurements quickly and accurately; you always have an ample reference face against your work without having to flip the square. This also simplifies working in two axes at once (e.g., measuring in 50mm and over 40mm), substantially reducing the chance of error when measuring and marking two dimensions.
The stainless steel blade is 75mm wide and 150mm long, machine ground on all four edges and graduated to 100mm along both edges and across one end to 70mm.
The diamond cut-out in the blade holds a pencil tip in position and makes it easy to draw lines parallel to an edge. The locking mechanism has a notched pin like those on combination squares, with the blade bearing on polished, hardened steel reference pins set in the body. Accurate and well made.