• Each set consists of an inside micrometer head and a series of fully hardened and lapped extension rods of different lengths all with carbide measuring faces • Anvil and spindle are hardened and precision ground with microlap finish on ends. • Spindle thread hardened, ground & lapped. • Microfine graduations on satin chrome. • Positive locking nut on spindle. • It is recommended that the inside micrometer with a rod be calibrated by a micrometer or ring gage. • Coiled spring pressure contact type rods are each marked with appropriate length. • Quick, easy zero adjustment on the sleeve. • Accuracy = .00005" x (3 + L"/2) • Meets or exceeds Federal accuracy specs.• Reference standard included with set. • Includes a wrench and a case