IEC 63267-1: 2023 covers enhanced macrobend loss 50 µm core diameter multimode fibre optic connection interfaces. It includes references, document structure details, definitions, and standardised optical connection grades. The grades are based on random mated connections between two optical connector populations according to prescribed characteristics including the core diameter and numerical aperture mismatches. This document describes the rules under which an optical interface is created. It also defines standardised test methods where appropriate.