Model AT-8 is especially designed to hold interchangeable high speed and carbide insert threading blades. When the cutting blade is mounted on the upper surface of the holder and the spindle direction is reversed, thread cutting can be accomplished without danger of hitting shoulders thereby speeding up threading operation. Lead angle adjustment is obtained through set screw changes. Various pitches of precision ground high speed steel threading blades for cutting American standard 60 degrees and Acme 29 degrees. Threads are available. Carbide inserts conveniently mount in place of the high speed blade when required.