A dose setting mechanism for a drug delivery device is disclosed. The mechanism comprises an outer housing and an inner housing having an external groove. The inner housing guides a driver having either a blocking or locking member disposed inside the driver that can lock a flexible tab to an internal groove during dose delivery in the inner housing such that the driver follows the path of the groove and to advance a spindle to move a cartridge bung. A dial sleeve is disposed between the outer and inner housing and is rotatably engaged with the inner housing.