This line of Professional T-Squares feature a 2" wide extruded aluminum blade with dual inking edges calibrated in inches and centimeters. Calibrations are made using a photo anodizing process giving them smooth, tick-free finish that will not wear. The black ABS plastic heads are light-weight and virtually unbreakable. The heads are secured with five screws instead of rivets. Unlike the Standard T-Square, the Professional aluminum blades have channeled backs that glide easily on drafting tables.