The new version of the International Standard ISO 3442-1 has been prepared by Technical Committee ISO/TC 39 "Machine tools", Subcommittee SC 8 "Work holding spindles and chucks". Germany was involved in the preparation of this standard through Working Committee NA 121-02-07 AA "Drehmaschinenspannzeuge und Zubehör" ("Lathe chucks and accessories") of the Tools and Clamping Devices Standards Committee (FWS). This part of ISO 3442 specifies the sizes for interchangeability of self-centring, manually operated chucks with two-piece jaws (tongue and groove type) and describes, by reference to ISO 230-1, the geometric tests for such chucks. It also specifies the tolerances which apply to these tests. For geometric testing, only the verification of the rotational accuracy of the chuck and the positioning of the assembling elements of the top jaws are dealt with.