A blow mold assembly comprises removable neck insert mold components for forming features of a container for engaging a removable container closure and manually operable retention devices for releasably retaining the neck insert mold components with mating mold components of the mold assembly. Advantageously, each manually operable retention device comprises a clamp mechanism comprising a lever arm and clamp arm arranged so that the clamp arm is rotated between a release position and a clamp position by manual operation of the lever arm and the clamp mechanism is effective to resist forces acting on the clamp arm to rotate the clamp arm to the release position when the clamp arm is in the clamp position. Each manually operable retention device is retained with an associated mating mold component when a neck insert mold component is removed from or installed to the mold assembly.