Abstract: In order to service work stations of either spinning or doubling machines of the type having several service units travelling alongside their work stations, whenever an inspection of a given service unit becomes necessary, the given service unit to be inspected is brought from an operative condition into an inspection position. Such position is crosswise to the usual operative direction of travel of the service unit, and its side to be inspected (and which is otherwise turned towards the machine) is preferably thereby rendered accessible. Also, its normal work path is opened to use by another service unit. Such other service unit then travels into the opened work path and takes over the task of servicing the work station or stations in the assigned operative work area of the given service unit being inspected until same is brought back from its inspection position into its work path upon completion of the inspection, and again assumes the task of servicing work stations of its assigned work area.