Straight threaded shanks in high-speed steel — the arbor that carries HTC's threaded-shank cutters. The plain end goes into your holder or collet; the cutter screws onto the threaded end and seats against the shoulder, which squares it to the axis and takes the cutting load.
Pick the shank by two things: the thread your cutter uses, and the shank diameter your holder takes. Threads from 5/16-24 to 1-1/4-12, shanks from 1/4" to 1".
