The Klein 31650 Hole Saw Arbor is 1/4-Inch round with 1/2-Inch-20 threads, a 118-degree split point pilot bit, and a hardened mandrel for long thread life. For use with Klein hole saws: 5/8-Inch - 1-1/8-Inch. Chuck Size: 1/4-Inch. Shank Style: Round tri-lobe. Shank Size: 1/4-Inch. Thread Size: 1/2-Inch-20. Note: Read and follow safety instructions in power tool owner"s manual.