Inside Micrometer Specifications - Measuring range: 5mm~30mm, Accuracy: 0.01mm, Clear laser marking line for convenient reading. (Note: There is no need to calibrate the micrometer during common use. The micrometer only needs to be calibrated when it is severely worn.) Locking Device & Ratchet Stop Device - Designed with a locking device, the precise machine structure makes it more intuitive and convenient to read, the built-in ratchet stop device ensures accurate repetitive readings High-quality Materials - The main body of the micrometer is made of stainless steel with a chrome-plated surface, wear-resistant and durable. High-quality alloy measuring heads can be used for various internal size measurements, fine workmanship and no burrs. Package Contents: 1 x Inside Micrometer, 1 x Wrench, 1 x Calibration Ring, 1 x Packing Box.