of the conventional drill in a circular bore 128 which according to the present invention is provided for that purpose in the drill chuck 9a it should be appreciated by one skilled in the art that the key 125 in cooperation with the square notch 120 in the key plate 101 and the circular bore 128 in the drill chuck 9a prevents rotation of the individual down the hole drills 1 in the gang drill casing 100 the center drill 1c is of similar construction to the peripheral drills 1 and is provided with a modified drill chuck 1c and a modified backhead 3c the modified drill chuck 1c has an external thread 130 which cooperates with a threaded bore 131 in the key plate the threaded combination retains the center drill in the gang drill casing the backhead 3c is provided with a centralizing boss 132 which is disposed in assembled configuration in the bore 109 which supplies pressure fluid to both the central drill and the peripheral drills in the gang drill combination pressure fluid is supplied from bore 109 to the central drill 1c through pressure fluid bores 107c provided in the backhead 3c in the preferred embodiment shown the drill bit 8a is of slightly larger diameter than the drill for the peripheral drills while the central drill 1c is provided with a drill bit 8c which is of approximately the.