Acme Threaded Rod
Acme threaded rod has a different thread style than normal threaded rod.  The trapezoidal threads in an acme replace the triangular threads found in standard threaded rod.  Acme rod allows for an increase in power of motion because of this thread style and creates a smoother sliding ability.  Threads are less likely to be deformed because of the shape.

Left hand threaded rods differ from standard threaded rod because the threads run the opposite direction.  These are used to join materials together where counterclockwise movements would back out the right handed threaded rod.  The threaded rod is used where longer applications are needed.