Abstract: A cylindrical beam-type micrometer measurement system is disclosed having an extended-length measuring range of 0-100 inches or more, and an accuracy of approximately 0.000005 inches (5 microinches), and which is designed as a retrofit to the widely-used Mechanical Supermicrometer, Model A, manufactured by Pratt & Whitney. In order to maintain accuracy with a 10-foot cylindrical beam, one or more center pedestals are used to support the middle portion of the beam, and a modified tailstock housing is moveably secured to the beam using a dovetail slot and clamp configuration. This arrangement allows the tailstock to be freely moved over the center pedestals to accommodate objects of different lengths. A displacement meter probe adapter assembly is also provided, which permits a Mechanical Supermicrometer tailstock to be used with an electrical displacement meter and probe.