Abstract: Methods and apparatus for making a connection that can be rotationally locked by expansion are disclosed. Threaded tubular ends include a slot cut across a thread at a location along the circumference of the thread. Threading two tubular members that have the slot disposed in either or both of a pin or box end of the tubular members establishes the connection. The slots represent no impediment to the make-up or break-out of a box by pin connection prior to expansion. During expansion of the connection, the threads of either the box or pin end are forced via plastic flow into the slot in the corresponding thread. This results in locking the connection and preventing relative rotation between the two tubular members, which could otherwise loosen the connection.