The Faithfull Three-Square Second Cut Engineers File (sometimes described as a triangular file) has three flat sides and is used to file in acute internal angles, clean cut square corners, enlarge and clean up angular holes and sharpen serrated jaws and saw teeth. Fitted with a comfortable grip, it is ideal for professional and frequent DIY use. The FAIFITSSC6 Engineers' File has the following specifications: Cut: Three-Square Second. Blade Length: 150mm (6in). Blade Width: 13mm (1/2in).