note that as the button drive mechanism 39 moves forward a feature on the forward left side legs begins to drive the shuttle retention clips outward the shuttle retention clips have dowel pins at the pivot point at well as near the interface with the shuttle as shown in fig1 the dowel pins near the interface with the shuttle extend such that as the button drive mechanism legs move past the shuttle retention clips begin to unlatch from the shuttle fig1 shows that after the clips 42 unlatch the shuttle snaps forward to the left driven by the compression spring between it and the button drive mechanism throughout this portion of the stroke the driving clips are still held away from the rack fig1 illustrates the position of the clips 42 at the time the needle s will have punctured the skin during the snapping of the shuttle and syringe forward at this point in the stroke the dowel pins in the driving clips are close to a ramp in the rib that is holding them back fig1 shows the button drive mechanism has moved forward the dowel pins move down the ramp and the clips are allowed to interface with the drive rack fig1 shows as the stroke continues a dose is administered until a hard stop in reached in the system indicating end of dose once the button drive.