These Lenox Bi-Metal Hole saws are long lasting, fast cutting, and versatile. The Tuff tooth design is reinforced to cut stronger and last longer. These blades are long lasting due to the patented Vari-Tooth design resists tooth strippage. The Lenox Bi-Metal Hole saws stay sharp due to the high speed steel teeth that resist breaking and offer an extended life. These saws withstand high torque due to their thick backing plate with holes for drive pins which resist damage to high torque.