Abstract: A shrink disc, compression ring for a shrink disc, insert for interposing between a shrink disc and a shaft, and associated methods are provided. In each case, a serrated inner surface of the compression ring or insert is provided which is configured to grippingly engage the shaft. Protrusions of the serrated surface may mark or intrude into the shaft. The compression ring or insert may be provided in multiple arcuate parts for circumferential arrangement about the shaft. Various protrusion configurations, including symmetric and sawtooth, are provided. The shrink disc is generally operable to apply radially inward pressure to the shaft for example using a wedge effect.

Abstract: A cushion sub for absorbing both axial and torsional vibration in a drill string and including an outer casing connectable at one end to a section of a drill string, and an inner piston reciprocally mounted in a cylinder within the casing, the piston having a shaft projecting from the other end of the casing connectable to another section of the drill string. The cylinder includes a first cushion device at opposite ends thereof for engagement by the piston to absorb axial vibrations. A spline type connection prevents relative rotation between the piston and the cylinder. The cylinder is mounted for arcuate turning in a chamber within the casing, but the cylinder has vanes which are interposed between vanes fixed to the casing, and elastomeric material between the vanes of the cylinder and the vanes of the casing absorbs torsional vibrations being transmitted between the cylinder and the casing.