A downhole tool comprising: an inner mandrel (1, 7, 11, 15), an outer mandrel (14, 13, 12, 19), and a coupling mechanism (8, 9, 12; 7, 6, 5, 4) to couple the inner (1, 7, 11, 15) and the outer (14, 13, 12, 19) mandrel, the coupling mechanism (8, 9, 12; 7, 6, 5, 4) comprising a plurality of longitudinally elongate members acting between the inner (1, 7, 11, 15) and outer (14, 13, 12, 19) mandrel, wherein the longitudinally elongate members comprise cables having a longitudinal length substantially greater than their diameter; wherein the plurality of cables are arranged around the longitudinal axis of the downhole tool; the downhole tool further comprising a biasing device acting between the inner (1, 7, 11, 15) and outer (14, 13, 12, 19) mandrel, wherein the biasing device is a separate component from the plurality of cables; wherein the coupling mechanism (8, 9, 12; 7, 6, 5, 4) permits at least a certain degree of relative rotational movement between the inner (1, 7, 11, 15) and outer (14, 13, 12, 19) mandrels; characterised in that one end of the plurality of cables is securely mounted to the inner mandrel (1, 7, 11, 15) and the other end of the plurality of cables is securely mounted to the outer mandrel (14, 13, 12, 19); wherein the plurality of cables are substantially fixed in their longitudinal length when tension is applied to one end relative to another but substantially do not resist relative compressive longitudinal movement occurring between the inner (1, 7, 11, 15) and outer (14, 13, 12, 19) mandrels, and wherein the plurality of cables provide a differential in their reaction to tension and compression; and wherein the coupling mechanism (8, 9, 12; 7, 6, 5, 4) is arranged such that compression of the inner (1, 7, 11, 15) and outer (14, 13, 12, 19) mandrels results in compression of the plurality of cables without necessarily resulting in relative rotation of the inner (1, 7, 11, 15) and outer (14, 13, 12, 19) mandrels. an inner mandrel (1, 7, 11, 15), an outer mandrel (14, 13, 12, 19), and a coupling mechanism (8, 9, 12; 7, 6, 5, 4) to couple the inner (1, 7, 11, 15) and the outer (14, 13, 12, 19) mandrel, the coupling mechanism (8, 9, 12; 7, 6, 5, 4) comprising a plurality of longitudinally elongate members acting between the inner (1, 7, 11, 15) and outer (14, 13, 12, 19) mandrel, wherein the longitudinally elongate members comprise cables having a longitudinal length substantially greater than their diameter; wherein the plurality of cables are arranged around the longitudinal axis of the downhole tool; the downhole tool further comprising a biasing device acting between the inner (1, 7, 11, 15) and outer (14, 13, 12, 19) mandrel, wherein the biasing device is a separate component from the plurality of cables; wherein the coupling mechanism (8, 9, 12; 7, 6, 5, 4) permits at least a certain degree of relative rotational movement between the inner (1, 7, 11, 15) and outer (14, 13, 12, 19) mandrels; characterised in that one end of the plurality of cables is securely mounted to the inner mandrel (1, 7, 11, 15) and the other end of the plurality of cables is securely mounted to the outer mandrel (14, 13, 12, 19); wherein the plurality of cables are substantially fixed in their longitudinal length when tension is applied to one end relative to another but substantially do not resist relative compressive longitudinal movement occurring between the inner (1, 7, 11, 15) and outer (14, 13, 12, 19) mandrels, and wherein the plurality of cables provide a differential in their reaction to tension and compression; and wherein the coupling mechanism (8, 9, 12; 7, 6, 5, 4) is arranged such that compression of the inner (1, 7, 11, 15) and outer (14, 13, 12, 19) mandrels results in compression of the plurality of cables without necessarily resulting in relative rotation of the inner (1, 7, 11, 15) and outer (14, 13, 12, 19) mandrels.