A built-in dual purpose interposer device for a data storage device carrier mechanism is provided. The interposer device may fill empty or voided space in the carrier mechanism created when a data storage device is changed between a “direct plug” position, or first configuration, and an “interposer” position, or second configuration. The interposer device may be changed back and forth between the first and second configuration multiple times. When in the first configuration, the interposer device may provide structural support to a front end of the carrier mechanism and when in the second configuration, the interposer device may provide an internal mounting base for the data storage device at the base or bottom end of the carrier mechanism. The ability to interchange the interposer device may provide for a built-in base for attaching the interposer device without having to add in additional parts or costs.