These heavy-duty hole saws are constructed by welding a heat treated strip of high speed steel teeth to an alloy body and cap. That’s why they’re called “Bi-Metal”. This gives the hole saw teeth the ability to stand up to the high heat generated during the cutting process (without dulling prematurely) while the body is shatter-resistant for user protection. The teeth feature the Fastcut™ variable pitch tooth pattern which aids in the removal of metal chips or sawdust. These can be used on wood, metal, or even plastic. With a cutting depth of 1-5/8", they will cut through 2x4s – no sweat. When cutting metal, use a coolant for best results. These hole saws require the use of a separate arbor. Diameters 9/16" to 1-3/16" use arbor HS-OA01 while hole saws 1-1/4" and larger use arbor HS-OA10. Made in China.