This is a mortise lock that has an adjustable, spring-loaded hook latch projection for surface-mounted sliding patio doors constructed of wood, aluminum and vinyl with handle sets with vertical keyway position when in the locked position. It also fits doors using W&F manufactured handles. The mounting hole centers of this lock measures 3-11/16 in. on center, and the rear housing corners are square. Selection Tip: To ensure the perfect match is selected prior to purchasing, the lock will need to be removed to compare the following 4 features (besides the width of housing): 1) The distance of the mounting holes measured from center to center, 2) The faceplate ends; rounded or square, 3) The position of the slotted keyway when in the locked position; at 45-degree angle or vertical, and 4) The shape of the housing corners at the rear; square or slanted.