Abstract: In the percussion drill rod assembly of the present invention rotary force is transmitted through a tubular member of the assembly while impact force is transmitted through the rod member centrally located in the tubular member. Either of said rod and tubular members is provided with radially extending protrusions which guide said member with respect to the other member while enabling flushing medium to pass between said members.

Abstract: The invention relates to a drill bit for use in percussion drilling. The drill bit has a solid bit body, has cutting members on its face and a centrally disposed rod-receiving hole in its rear portion. The hole has, in part, a conical internal surface and a cylindrical internal surface in front of said conical internal surface. Said cylindrical internal surface is provided with an internal thread at a distance remote from the bottom of the hole. A cooperating drill rod has a forwardly tapering portion with a conical exterior face complementary to the conical interior surface in the hole of the drill bit and an external thread on its forepart.

Abstract: A drilling machine may include extension equipment comprising (a) drill rods -- connected end-to-end -- for transmission of impact force and (b) a system of tubular members -- likewise connected end-to-end -- surrounding said rods, for transmission of rotary force. Such extension equipment may be coupled to the machine per se by means of a tubular adapter threadably connected, at one of its ends, to the tubular members system and at its opposite end connected to the machine through polygonal coupling means.