This document provides the most important design and metrological characteristics of two-point inside micrometers: with a scale interval or digital step of 0,001 mm and 0,01 mm; with analogue or digital indication. It applies to two-point inside micrometers with and without interchangeable rods. This document does not apply to micrometers fitted with a dial gauge, or to jaw micrometers. NOTE Three-point inside micrometers are excluded from this document and will be covered by the part 2 of this document.