Abstract: A rock bolt shell and cone. An expansible shell having a cylindrical outer surface and raised ridges in relief on the exterior of the shell. One or more ridges are located along a curve non-congruent with a circumferential circle of the cylinder. In a disclosed embodiment, each ridge lies along a helix of the cylinder and ridges are paired such that the helix of a first extends in one rotational direction while the curve of a second of the pair extends in the other rotational direction. Each helix forms an angle of forty-five degrees with a center line of the cylinder. Ridges intersect such that "V"-shaped projections extend along the outside of the shell. The vertices of certain of the projections project a radially maximum amount while each of the legs of the "V" taper radially inwardly toward the cylindrical surface as the leg extends away from the vertex. The cone, threaded for installation on a bolt rod has one or more axial indentations to improve grout flow about an installed bolt.