Abstract: A cushion sub 10 including an input portion 130 for receiving drive from a drive means, and an output portion 60 for transmitting the drive to a drill string. One of the input portion 130 and the output portion 60 including one or more guides 70. The other of the input portion 130 and the output 60 portion being engaged with the one or more guides 70 for transmitting the drive and arranged for relative reciprocating sliding movement along the one or more guides 70 between a first and a second limit of movements. At least one of the one or more guides 70 including a shoulder 500 adjacent at least one of and between the first and the second limit of movement to minimise adverse step formation as the at least one guide 70 wears. One of the input portion 130 and the output portion 60 may define a cylinder 20, 50 including first end wall 40 and second endwall 50. The guides 70 might be formed by drive pins 70. The drive pins 70 may be press fitted to the first endwall 40.