A disk drive head stack assembly (66) of a configuration that facilitates the assembly thereof is disclosed. One or more head/arm assemblies (74) are mounted on a pivot bearing (118). This pivot bearing (118) includes a tapered section (126). Each head/arm assembly (74) may be mounted on the pivot bearing (118). Thereafter, a retainer ring (102) may be advanced relative to the pivot bearing (118). Advancement of the retainer ring (102) along the tapered section (126) expands the retainer ring (102) so that the same may be disposed within a retainer ring slot (130) of the pivot bearing (118). Each head/arm assembly (74) is maintained between this retainer ring (102) and a flange (134) of the pivot bearing (118).