System, including methods and apparatus, for treating orthopedic conditions using a rod member structured for placement in a medullary canal of a bone and including at least one locking aperture with an internal thread structure. In some embodiments, the internal thread structure may include two or more thread leads disposed adjacent the same end of the locking aperture, two or more interspersed internal threads, and/or a thread depth substantially less than that of a corresponding threaded fastener for the locking aperture.