Abstract: A down hole hammer assembly comprising a reverse circulation hammer (11) having a drill bit (12) mounted to one end of a housing which accommodates a percussive hammer, the other end of the housing being adapted to be mounted to a drill string, the assembly further comprising a support member (14) receivable on the lower end of a bore hole casing (13) which is receivable over the drill string, the support (14) comprising a first part (15) adapted to be fixed to the lower end of the casing and a second part (16) rotatably received on the first part (15) and capable of limited axial slidable movement thereon, the second part (16) being engagable with the drill bit (12) to be rotatable with the drill bit (12) on rotation of the drill bit (12) in one direction and to be movably axially with the drill bit (12) the drill bit (12) being disengagable with the second part (16) to be able to be movable axially relative to the second part (16), flow passageways being provided between the drill bit and the second part to