An adaptor for use in driving a pipe into the ground by a ground piercing tool, which adaptor is arranged to be driven by the piercing tool. The adaptor consists of a three piece cylindrical unit held together by two garter springs. A tapered conical bore, formed in the adaptor, has a slope comparable with the slope formed on the forward end of a ground piercing tool used therewith. A portion of the adaptor is arranged to enter the end region of a pipe being worked upon, and a circumferential shoulder is formed on the adaptor, for engagement with the end of the pipe. Impact action upon the piercing tool not only wedges the adaptor into tight engagement with the inner region of the pipe, but also results in driving action upon the pipe by reason of the circumferential shoulder being in engagement with the pipe end. When the piercing tool is subjected to reverse impact action, it is released from the adaptor, and the latter is collapsed by action of the garter springs, so that it can be withdrawn from engagement with the pipe.