This unique product is the most versatile locking unit available; it will accommodate 7 different hole spacing patterns from 2-11/16 inch to 6-7/8 inches. The 3-15/16" hole spacing is designed for use with mortise lock installations using Adam Rite and W & F mortise locks. These holes are offset 1/8" from that of the locking cylinder hole. The spacing allows locking unit to adapt to a variety of handle sets.