Abstract: A plurality of piston and cylinder assemblies extend radially from the wall of the drill tube above the drill bit. A roller assembly is journalled in the distal ends of the pistons and engages the wall of the bore hole. The pistons are urged outwardly by fluid pressure to engage the wall and they are inclined approximately 10.degree. from the longitudinal axis of the drill string so that when the drill string is rotated, the engagement of the inclined rollers against the wall urges the drill bit downwardly thus assisting in applying the required pressure to the rotating bit.