This part of ISO 12858 specifies the most important requirements of tribrachs used in geodesy for the connection of the instrument's body with its base. The requirements in this part of lSO 12858, however, do not guarantee the full interchangeability of the instrument's body with tribrachs of different manufacturers, but give the detailed specifications of the clamp system to ensure the reliable mounting and clamping without prejudicing their performance and their usefulness. There are mainly two types of tribrach in use, categorized in this part of ISO 12858 as Types W and Z. This part of ISO 12858 is applicable to tribrachs which are used for levels, theodolites, tacheometers, GPS equipment, EDM instruments and in combination with targets, reflectors, antennae etc.