Hammer drill

A hammer drill including a cylinder; a piston and a ram mounted within the cylinder; a drive mechanism for converting rotation of a motor into reciprocating movement of the piston; a ram driven by the piston via an air spring; at least two air entry points formed through the wall of the cylinder in different axial positions along the length of the cylinder, each of which are capable of replenishing the air spring; the ram striking a tool in a tool holder; wherein there is further provided a selector mechanism which selectively opens and close the air entry points; characterized in that the selector mechanism opens only one air entry point at any one time during normal use, the selector mechanism closing all other air entry points, each of the air entry point capable of replenishing the air spring during normal use when opened by the selector mechanism.