This is a Snap On Offset Box Wrench. Size is 5/16" x 3/8". Part number XSO1012 . Overall length is about 4.5 inches. There are sanding marks on the front and back where numbers were removed by the previous owner (standard US Military de-marking process). Some wrenches have tape residue on the sides. Otherwise, good to very good condition.
The items pictured are examples of what you will receive.