The air hammer is of the type employing a body hav- ng a first portion (1) with a central bore (20) and a piston 21) reciprocable in the bore (20) by pressurised air under control of an automatic valve (25). The body has a second or muffler portion (7) which embraces the first portion (1) and is operative to muffle the noise created by exhaust air rom the bore (20). The muffler portion (7) is provided with pressurised air passage means (59) through which the pressurised air must pass for causing operation of the piston (21). The passage means (59) are so arranged that removal of the muffler portion (7) from the body (1) dis- upts the supply of pressurised air to the piston (21) and :hereby renders the hammer inoperative. Headers (2, 4) are provided on the ends of the first body portion (1) and are drawn tightly against the ends of this and muffler portion (7) by tie bolts (57, 58) which extend through the passages (59, 60) respectively, in the muffler portion (7). The passages (59, 60) are of larger diameter than the associated bolts (57, 58) and the clearance space between one of the through passages (59) and the associated bolt (57) acts to deliver live air to the piston, to accumulate pressurised air. and to deliver pressurised air for actuating the automatic valve (25).