A downhole tool string component that includes a tubular body with an inner surface, an outer surface and a shoulder extending from the outer surface at one end of the tubular body, a sleeve disposed about the outer surface having an end face in contact with the shoulder. The downhole tool string component further includes a loading member disposed about the outer surface near the other end of the tubular body and which is adapted for loading the sleeve against the shoulder. The loading member includes an internal threadform that is adapted to threadingly engage an external threadform formed into the outer surface of the tubular body. At least one of the external threadform and the internal threadform includes a plurality of threads with a distal thread having a first thread height and a proximal thread has a second thread height, with the first thread height being greater than the second thread height and a plurality of the threads heights between the first and second thread heights continuously tapering from the first height to the second height.