A rheometer system (100, 200) comprising: one or more posts (104, 106) extending between two plates (102, 112); a cross-head mounted on the posts (104, 106), the cross-head being movable along the posts (104, 106); a drive apparatus which moves the cross-head upwardly and downwardly along the posts (104, 106); an upper die disposed on the cross-head; a lower die disposed in spaced relation to the upper die, the upper and lower dies (74, 72) being configured to capture a test sample therebetween; and; apparatus for coupling the drive apparatus to the cross-head to accommodate misalignment between the drive apparatus and the posts (104, 106) upon which the cross-head moves and to permit alignment of the upper die with the lower die, the coupling apparatus comprising: a connector having a shaft coupled to the drive apparatus, and a head enlarged with respect to the shaft, the head having a curved surface; a flange disposed on the cross-head, the curved surface of the head bearing against a surface on the flange; and a retainer having a lip overlying the head of the connector to limit upward movement of the head with respect to the surface of the flange, the lip of the retainer being spaced sufficiently from the connector to permit tilting movement of the connector with respect to the cross-head while still retaining the connector within the retainer as the cross-head moves upwardly and downwardly. one or more posts (104, 106) extending between two plates (102, 112); a cross-head mounted on the posts (104, 106), the cross-head being movable along the posts (104, 106); a drive apparatus which moves the cross-head upwardly and downwardly along the posts (104, 106); an upper die disposed on the cross-head; a lower die disposed in spaced relation to the upper die, the upper and lower dies (74, 72) being configured to capture a test sample therebetween; and; apparatus for coupling the drive apparatus to the cross-head to accommodate misalignment between the drive apparatus and the posts (104, 106) upon which the cross-head moves and to permit alignment of the upper die with the lower die, the coupling apparatus comprising: a connector having a shaft coupled to the drive apparatus, and a head enlarged with respect to the shaft, the head having a curved surface; a flange disposed on the cross-head, the curved surface of the head bearing against a surface on the flange; and a retainer having a lip overlying the head of the connector to limit upward movement of the head with respect to the surface of the flange, the lip of the retainer being spaced sufficiently from the connector to permit tilting movement of the connector with respect to the cross-head while still retaining the connector within the retainer as the cross-head moves upwardly and downwardly. a connector having a shaft coupled to the drive apparatus, and a head enlarged with respect to the shaft, the head having a curved surface; a flange disposed on the cross-head, the curved surface of the head bearing against a surface on the flange; and a retainer having a lip overlying the head of the connector to limit upward movement of the head with respect to the surface of the flange, the lip of the retainer being spaced sufficiently from the connector to permit tilting movement of the connector with respect to the cross-head while still retaining the connector within the retainer as the cross-head moves upwardly and downwardly.