13MA Starrett Double Square with Graduated Hardened Blade: 100mm
These squares are very popular with machinists, toolmakers, and pattern makers. The sliding blades are adjustable making it practical for a wide variety of uses. The faces of the head are ground square, and the 6" (150mm) size has a level.
A drill grinding blade, also available for 6" (150mm) squares, is beveled to 59º for drill grinding on one end and 41º (the cutting angle of countersinks for machine screws) at the other. Both ends have quick-reading 64ths grads. and the graduation is located to measure perpendicularly to the axis of the drill. By reading the graduations, the center point can be easily and accurately located.
Starrett Series 13 & 13M Double Squares