Fluid delivery devices and means for engaging components therein are described. The devices may include a plunger positioned within a reservoir and connected to a non-rotating drive screw and a drive nut capable of engagement with the drive screw, where, upon engagement of the drive nut with the drive screw, rotation of the drive nut linearly displaces the drive screw. The devices may also be skin-securable and comprise a reusable part and a disposable part wherein, upon connection of the reusable part and the disposable part, the drive screw engages with the drive nut such that rotation of a motor and/or one or more gears results in rotation of the drive nut and linear displacement of the drive screw.
