to the open central portion of the drill rod assembly 9 lubrication of the bearings is readily provided by means of an axially extending bore 64 and a lateral passageway 65 which is fed through a grease fitting 66 in a fashion well known to those skilled in the art the outer barrel head 50 a is coupled to a portion of the drill rod section 40 by means of a connector 68 which has threads 69 and 69 a at either end thereof for engaging corresponding threads in the drill rod section 40 and the outer barrel head 50 a the connector 68 is provided with a central bore therethrough which allows the passage of the orienting rod 11 as well as sufficient area for the passage of drilling fluid through the drill rod section 40 as will be explained in greater detail below each additional drill rod section 40 needed to provide the proper length may be coupled onto the drill rod section 40 and to each other by means of the same connector 68 or by a different connector as required in use a driving means namely the rotary spindle 10 fig7 at the upper end of the drill pipe assembly 9.