This International Standard specifies the dimensional characteristics and concentricity tolerance requirements for three-jaw keyless type, self-tightening drill chucks with taper bore or internal thread mounts. It also applies to three-jaw keyless type, hand tightening drill chucks with internal thread mounts. Three classes of chucks are specified, namely: • — Heavy (H) • — Medium (M) • — Light (L) for use in various fields of activity.