ake errors and guesswork out of your next drywall job with this heavy-duty 48 T-square from Johnson. Its extruded aluminum blade is 3/16 thick creating a safer straight edge that prevents your utility knife from slipping while its clear protective anodized finish will keep your tool safe from rust and corrosion. The JTS48HD T-square features a unique rivet assembly that permanently bonds the head and blade so that it stays square for life. This T-square was also designed to be easy to use. It features thermal-bonded black 1/8 graduations that are large and bold for easy reading.