HAC555 Annular cutters from HAC555-O which is a combination of "Weldon-shank" and "Universal Shank" Annular cutters. It has set 90 Flats for grub screws in tradional "Weldon-Shank" machines and one-touch grooves for Quick connect. Otoaworks annular cutters are superior with it's quality which provide 2x life and the fastest cut. It fits into 90% of Magnetic drilling machines, as well as other stationary machines. A special formula used in the cutters, reduces the risk of breakages.