Features [High precision] Built-in ratchet stop device to ensure accurate repeated readings. [Easy to read] Clear marking lines, easy to read. [Easy to read] The hole micrometers is designed with a locking device, and the precise mechanical structure makes it more intuitive and easier to read. [Fine workmanship] High-quality alloy measuring heads can be used to measure various internal dimensions, with fine workmanship and no burrs. [High quality material] The main body of the internal micrometer is made of stainless steel, and the surface is chrome-plated, wear-resistant and durable Specifications: Type: Inside micrometer Measuring Range: 5mm~30mm Material: Stainless steel Precision: 0.01mm Weight: 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 0 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 0 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 0 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 Micrometer 1 x Wrench 1 x Calibration Ring 1 x Packing Box Note: Please note that the new type and old type of this product will be sent randomly, and make sure you will not mind before ordering. Package List