Features The main micrometer body is made of stainless steel with chrome plated surface, wear-resisting and durable Designed with locking device, precise machinery structure make it more intuitive and convenient to read High quality alloy measuring heads can be used for various internal size measurement, fine workmanship and no burr Clear laser marking line for convenient reading Built-in ratchet stop device ensures accurate repetitive readings Specifications:Type: Inside micrometerMeasuring Range: 5mm~30mm Material: Stainless steelPrecision: 0.01mmWeight: 268g(approx.) Zeroing: Clean the surface of measuring anvil heads with a soft cloth, then rotate measuring device to make two measuring surface contact. If two zero lines of differential sleeve and fixed barrel do not alignment, use the following two methods to adjust. Method I, if the error is less than 0.02mm (0.001"), use ratchet stop to lock screw tightly, then use wrench to pull fixed barrel till two zero lines alignment. Method II, if the error is greater than 0.02mm (0.001 "), Step1, use ratchet stop to lock screw tightly, then use wrench to loosen the ratchet stop  and remove differential sleeve. Step2, re-align zero lines of fixed barrel and differential sleeve, then put ratchet stop back on. If necessary, adjust it again using method I. Note: There is no need to calibrate micrometer during common use. Micrometer only need calibration when it is severely worn. Package Includes:1 x Inside Micrometer1 x Wrench1 x Calibration Ring1 x Packing Box Package List