Rules:

Rule: The Preceding Process must Always Produce its Parts in the Quantities Withdrawn by the Subsequent Process

It is a rule which says that processes must never overproduce parts in any quantity, for this is a waste of labour and materials.

Rule: Defective Parts Should Never be Conveyed to the Subsequent Process

This rule concerns the quality of the parts moved by the Kanban. In a Just-In-Time system, there is an absolute ought to maintain high quality in the production of parts and subassemblies as there are no buffer inventories to cover for defective parts.

Rule: Process the Kanbans in Each Work Center Strictly in the Order in which They Arrive

While a work centre has in its mailbox several Kanbans from different processes, the operators in that work centre must serve the Kanbans in the order in which they arrived.