What is a Cummins Injector Cup and What Is Its Purpose? The Cummins Injector Cup (often referred to as the injector sleeve or injector tube) is a precision-machined cylindrical component that is pressed into the cylinder head. It serves as the socket that houses the fuel injector and creates a critical barrier between the fuel system and the cooling system. What does it look like? It is a brass or steel tube with a precision-machined bore that matches the outside diameter of the injector. It has a flanged top that seats against the cylinder head and a tapered or radiused bottom that extends into the combustion chamber area. https://www.cq-longshine.com/cummins-injector-cup