A retention knob for use with a tool holder that is less prone to distorting a tapered tool holder surface, especially if it is over-tightened. The retention knob includes a knob head, a flange engageable with an end of a tool holder shank, a pilot segment receivable by the counter bore defined by said tool holder shank and a threaded segment spaced from said flange by an undercut segment. The threaded segment is configured so that it has a length that is substantially the minimum length required to achieve maximum thread holding strength. The undercut segment is configured to space the threaded segment from its head so that a distal end of the threaded segment is substantially near the bottom of the tapered bore forming part of the tool holder. With the disclosed construction, an upper portion of the threaded tool holder bore is not engaged by the threaded segment. The threaded segment has balanced threads which is achieved by locating the lead-in of the thread 180 from the lead-out of the thread. Chamfer angles at the lead-in and lead-out of the threaded segment are controlled to be the same or substantially similar.

A retention knob tool. A tubular body is held in a tubular sleeve, and symmetrically formed around an axis. The tubular body also has an internal bore. Four locking ball retainer sockets are formed in the tubular body. A retention knob aperture is recessed within a top plate. Four balls are movably held in the ball retainer sockets. A tubular end stop is affixed to the tubular body rearward end. A drive tool cavity is recessed within the tubular body rearward end. The sleeve forward end includes a recessed circumferential portion bounded by a first thicker portion of the inside wall, where the first thicker portion bears against the balls when the tubular body is translated rearwardly not an inward lock position and the inward force is removed from the plurality of balls when the tubular body is extended forwardly into a released position.