A dose setting mechanism (4) for a drug delivery device (1) is disclosed. The mechanism comprises an outer housing (40) and an inner housing (44) having an external groove (62) and a helical spline (68). The inner housing helical spline guides a driver (30) to dispense a set dose. A dial sleeve (10) is disposed between the outer and inner housing and is rotatably engaged with the innet housing. When a dose is set, the dial sleeve is rotated and translates away from both the outer housing and the inner housing.
