A method of securing an assembly (101) of a drug delivery system, comprising: configuring at least a first component (202, 204, 206, 208) and a second component (210) of the assembly (101) in a closed configuration ready for placement into the drug delivery system; installing an assembly key (150) including a locking element on the assembly (101) to secure the assembly in said configuration; and, transporting the assembly (101) with the assembly key (150) installed. (Fig. 2)