An assembly for an infusion device that delivers fluid to a user is disclosed. The assembly includes a reservoir and a piston actuator. The reservoir includes a body section having a fluid chamber, a fitting section extending from the body section, a housing lock structure to couple the reservoir to a housing of the infusion device, and a piston located within the fluid chamber. The housing lock structure inhibits axial movement of the reservoir relative to the housing. The piston is movable relative to the body section, and it has a tip section facing the fluid chamber and a base section opposite the tip section. The base section has an actuator lock structure. The piston actuator controls axial movement of the piston within the fluid chamber, and it has a piston lock structure that cooperates with the actuator lock structure to removably couple the piston to the piston actuator.
