The role of supplier is moving from component supplier to information and knowledge supplier. Designers must rely on suppliers for expertise throughout the engineering design process. Due to this trend the customer-supplier interface now plays a key role in the design and development of new products. Paper looks at the interface through the linkage of process models and product information. Paper confirms previous results that design process models rarely aid designers in their decisions on supplier interactions. My research helps bridge that gap by providing detailed examples of the communication in these interfaces for the practitioners. The main result of the paper is the identification of the importance of parameters in collaboration in customer-supplier relationships. The case company terms critical parameters as “killer parameters”, which are “critical component attribute values, which must be kept within a certain value range or below a certain maximum value because otherwise extensive reworking of the entire bogie system design would be required” They have extensive impact on components and they should be managed carefully by the customer and supplier. Thus these parameters require extensive communication in the interface to achieve consensus regarding the components’ properties. The railcar bogie can have 300 killer parameters. Focusing on the killer parameters could provide support during the assessment of engineering change effects.