While every step in a systematic approach to the design of an assembly for integral attachment using snap-fit features is important, none is more important than the selection of locking features. After all, it is these features that hold the assembly together. Comprised of a latch and catch component, locking pairs must themselves be selected using a systematic approach. This paper presents that approach as a six-step methodology, after defining and describing latch and catch components. It then demonstrates the methodology using a case study taken from real life.