To coat several cap-shaped substrates simultaneously in an economical way with the same and high quality, several coating chambers are connected into a cap coating station by a symmetrical gas line system with a common gas generator and by another gas line system with a common vacuum pump. The gas lines have a cross sectional area Q.sub.A (x) and a cross sectional form Q.sub.F (x) which as a function of the distance x from the gas generator or from the vacuum pump are substantially the same. In this way, the same flow conditions are assured in all coating chambers. The gas line systems can be formed by precision pipes or by a stack of solid plates, in which gas ducts are introduced by boring or milling. Several cap coating stations, which are connected by suitable symmetrical gas line systems with a common vacuum pump and a common gas generator, can be combined to form a unit.