A housing body (206) for a fluid delivery device comprises:an exterior and an interior and a syringe cartridge aperture (226)a pinion housing (208) attached to the interior of the housing body, the pinion housing having a pinion receiving aperturea pinion (210) which is received by the pinion receiving aperture, and attached to the pinion housing such that it can rotate within the pinion receiving aperture, the pinion comprising a front section having gear ridges, a syringe cartridge receiving aperture, and a rear sectionand a trigger portion (214) having a tab section (250) which is adapted to engage with the gear ridges (224) of the pinion when depressed.
