Abstract: A drill string anchor for use in a well bore, the anchor having a body, a through bore and a plurality of anchor assemblies, each assembly comprising an anchor member, a piston supported within a body and a biasing means. The piston is initially radially movable in response to an initiating fluid pressure in the through bore causing its movement from a first retracted position to a second extended position in which the piston drives the anchor member into contact with the wall of the well bore. The biasing means acts to provide a force biasing the piston towards the first retracted position.

Abstract: A drill string component for preventing chafing of a drill casing as a result of contact between the drill casing and a rotating drill string comprises a central mandrel (2) having rotatably mounted thereon a sleeve (11). The sleeve (11) is retained between shoulders defined on the mandrel to prevent accidental loss of the sleeve in the event of excessive wear in the supporting bearings. Axial thrust loads are transferred from the outer sleeve (11) to the mandrel by way of thrust bearings supported on the mandrel shoulders. Seals (24A, 24B) located between the outer sleeve seal bodies (23) and an inner sleeve (9) prevent the ingress of contaminants to the zone of bushings (12, 13) which rotatably support the outer sleeve.

Abstract: A tool for use in an oil or gas well to retrieve a drilling or production string from the well, said tool comprising an assembly which can be mounted on a supporting string, a driven member carried by the assembly and responsive to vertical movement of the assembly, to be driven in a predetermined rotational direction, said driven member being provided with or supporting a self-tapping thread provided at the lowermost end of the assembly, the self-tapping thread having the same sense as said predetermined direction of rotation.