Abstract: The invention is a transmission sleeve for the reverse cirulcation down hole hammer activated by fluid under pressure, the hammer including an outer hammer casing, a drill bit retaining means (17) and a drill bit (10) retaining means (17) and extending forwardly therefrom. The transmission sleeve (25) comprises a transmission sleeve retaining means to retain the transmission sleeve (25) to the hammer, a flange (28) to direct exhaust fluid from the hammer extending from the transmission sleeve retaining means towards the cutting face (14) of the drill bit (10) so that the exhaust fluid is directed towards the cutting face (14) and a chamber (30) that extends circumferentially around the drill bit (10) into which the exhaust fluid flows prior to discharge from the end of the flange (28).