An anchor mechanism for gripping wellbore casing, comprising: a tubular body having a central bore between an inlet and a first outlet, the inlet and first outlet being adapted for connection in a work string to be run into the casing; a recess provided in and around an outer surface of the tool body; a cone arranged in the recess, the cone having an outer surface including a first profile, the first profile having at least one ramp (86a,b); a plurality of selectively operable slips (90a-d), each slip having an outer surface configured to grip an inner surface of the casing and an inner surface including a second profile, the second profiling mating with the first profile in a first configuration; piston means operable to move the slips over the cone between the first configuration wherein the slips are located within the recess, a second configuration wherein the outer surface of the slips contacts the inner surface of casing of a first standard diameter; and characterised in that: the cone is a split cone, of two-part construction, as the cone is split longitudinally in two halves (70a,70b); and the piston means is operable to move the slips over the split cone to a third configuration wherein the outer surface of the slips contacts the inner surface of casing of a second standard diameter; wherein the first standard diameter and the second standard diameter are at least two successive standard diameters of wellbore casing, the standard diameters for casing being selected from a group comprising: 5", 5 1/2", 6", 6 5/8", 7", 7 5/8", 8 5/8", 9 5/8", 10 3/4", 11 3/4", 13 3/8", 14", 16", 18 5/8" and 20" (wherein 1 " = 2.54cm). a tubular body having a central bore between an inlet and a first outlet, the inlet and first outlet being adapted for connection in a work string to be run into the casing; a recess provided in and around an outer surface of the tool body; a cone arranged in the recess, the cone having an outer surface including a first profile, the first profile having at least one ramp (86a,b); a plurality of selectively operable slips (90a-d), each slip having an outer surface configured to grip an inner surface of the casing and an inner surface including a second profile, the second profiling mating with the first profile in a first configuration; piston means operable to move the slips over the cone between the first configuration wherein the slips are located within the recess, a second configuration wherein the outer surface of the slips contacts the inner surface of casing of a first standard diameter; and characterised in that: the cone is a split cone, of two-part construction, as the cone is split longitudinally in two halves (70a,70b); and the piston means is operable to move the slips over the split cone to a third configuration wherein the outer surface of the slips contacts the inner surface of casing of a second standard diameter; wherein the first standard diameter and the second standard diameter are at least two successive standard diameters of wellbore casing, the standard diameters for casing being selected from a group comprising: 5", 5 1/2", 6", 6 5/8", 7", 7 5/8", 8 5/8", 9 5/8", 10 3/4", 11 3/4", 13 3/8", 14", 16", 18 5/8" and 20" (wherein 1 " = 2.54cm). the cone is a split cone, of two-part construction, as the cone is split longitudinally in two halves (70a,70b); and the piston means is operable to move the slips over the split cone to a third configuration wherein the outer surface of the slips contacts the inner surface of casing of a second standard diameter; wherein the first standard diameter and the second standard diameter are at least two successive standard diameters of wellbore casing, the standard diameters for casing being selected from a group comprising: 5", 5 1/2", 6", 6 5/8", 7", 7 5/8", 8 5/8", 9 5/8", 10 3/4", 11 3/4", 13 3/8", 14", 16", 18 5/8" and 20" (wherein 1 " = 2.54cm).