The rear wheel is a drilled polyethylene ball held in place with a cotter pin. The lock may be further secured with a cotter pin. The British definition of "cotter pin" is equivalent to U.S. term "cotter". On July 7, BC Ferries concluded that a missing cotter pin was to blame. The nut is then secured with a split pin/cotter pin, R-clip or safety wire. On July 7, 2005, BC Ferries concluded that a missing cotter pin was to blame.