The Faithfull Engineers Square has been carefully crafted from high quality tool steel, these squares are accurate to BS939 Grade B standard. The stock and blade are precision ground to ensure straightness and accuracy, and the spring steel blade is hardened and tempered for increased durability. Size 150mm (6in) External size 173 x 100mm Internal size 150 x 75mm Stock thickness 11mm Blade thickness 1.7mm