This Standard pertains to the standardization of a basic tool holder shank and retention knob for numerically-controlled machining centers with automatic tool changers. The requirements contained herein are intended to provide tool holder interchangeability between machining centers with automatic tool changers of various types. The dimensions for cone-angle control are in accordance with the International Standard ISO-1947. This Standard will improve the understanding of the “CAT” toolholder, its associated components, and nominal operational values. It unifies the principle components of the basic machine tool holder interface—toolholder shank and spindle receiver geometry, pull stud, and conical taper information—into a single-source reference, providing instant access to information. This new information also eliminates ambiguities and establishes absolutes for all aspects of the toolholder/spindle interface.