A Pair Casement is a Casement window with two sash that operate inside a frame. In a Pair Casement the sash is typically configured to swing on the sides so one sash swings on its left while the other swings on its right. A Pair Casement can have sash that swing in or out. They can use a crank mechanism to swing out or they can be butt hinged to swing in or out. The locking mechanism is based on the operating mechanism.