Abstract: A locking pipe sub is disclosed including a threaded pin connection for engaging, for example, a pipe stuck in a well bore. The threads on the pin are formed in two sections which are adapted to align upon initial make-up of the sub to the stuck pipe, but to misalign, both axially and radially, when reverse torque is applied to the sub. The result is to create axial and radial forces between the threads of the sub and the threads of the stuck pipe which positively lock the sub against disconnection from the pipe except with the use of a releasing tool.