A rock drilling shank adaptor has at least one flush hole extending radially through the body of the adaptor in communication with an axially extending internal bore. The flush hole in a direction from an external side to an internal side includes a surface at a rearward region that is curved at least at a radially inner portion to extend in an axial direction towards a forwardmost end of the adaptor to increase the resistance of the adaptor to stress concentrations whilst achieving a desired flow rate of flushing fluid flow into the internal bore.