Amana Tool 56275 Carbide Tipped Mortising Screw Straight No Shear Cutter 5/16 + 0.015 D x 1/2 CH x 1/4 - 28 Thread
Designed for use in standard lock mortising tools, these cutters can also be used in a standard router if mounted on a separate arbor.
For 1/2" shank use arbor #47614.
#55255 uses arbor #47616.
View all available Threaded Arbors for Screw Type Mortising Cutters.
Please note that these are the cutters only! The below tools do not include the arbors.