(in machine building), a device for periodically turning (or shifting) articles or machine subassemblies by various fractions of a revolution or to various segments; used for processing or measuring the surfaces of articles that are positioned at an angle to the direction of one of the operating motions of the equipment or to the base plane of the mounting, as well as to inscribe divisions on linear and circular scales of instruments and machine parts.
A distinction is made between manual and mechanical index devices on the basis of their principle of operation. The most common type is the index head. Index devices also include various mechanisms and attachments for periodic rectilinear feed and rotation of tables, drums, and turrets of metal-cutting machines, rotation of the spindle units in multiposition machines, and change over from the cutting stroke to idling (and vice versa). As a rule, index devices have a ratchet mechanism and a revolving disk (dial) with reference holes or divisions; for more accurate operations they may be equipped with a reading device.