A dose setting mechanism for a drug delivery device is disclosed. The mechanism comprises an outer housing (17) and an inner housing (5) having an external groove (30； 31). The inner housing guides a driver (7, 9) having either a blocking or locking member (11； 11') disposed inside the driver that can lock a flexible tab (21) 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 (3) is disposed between the outer and inner housing and is rotatably engaged with the inner housing.
