A machining center must be capable of performing different types of machining operations by automatic tool change from a magazine or similar storage unit, and must have at least milling capability. A milling machine — even one with CNC control — that lacks automatic tool-change capability from a magazine is classified under the heading for milling machines rather than here.

A dedicated transfer line that moves workpieces through a series of fixed-station machining heads is a multistation transfer machine (845730). A flexible machining center that repositions the workpiece or changes tools to perform multiple operations at one station is classified under 845710. The key is whether the machine architecture is fixed-station sequential or single-station multi-operation.