traversing plate
Webster's Dictionary (GCIDE)
Traversing \Trav"ers*ing\, a. Adjustable laterally; having a lateral motion, or a swinging motion; adapted for giving lateral motion. [1913 Webster]
Traversing plate (Mil.), one of two thick iron plates at the hinder part of a gun carriage, where the handspike is applied in traversing the piece. --Wilhelm.
Traversing platform (Mil.), a platform for traversing guns. [1913 Webster]