An inside micrometer, also known as an internal micrometer, is a precision instrument for measuring the inside dimension of an object, such as the diameter of a hole or the width of a groove. A micrometer caliper with the points turned outward for measuring the internal dimensions of an object. FEATURES:Wide range of ID measurements with interchangeable rods.Each interchangeable rod is marked with its measuring range.The sizes of interchangeable rods can be adjusted with spacing collars.Both micrometer head and furnished rods are satin-chrome finished throughout.Internal Micrometer ManualSPECIFICATION:Metric ModelAccuracy: ?(6+L/50)?m*L=Maximum measuring length (mm) Fraction rounded upInch Model?(.00024+(.00004xR/2in)R=Maximum measuring length (inch)Fraction rounded upGraduation: 0.01mm or .001?