Dimension A = the lock length = functional length
Dimension B = the cam length
Dimension C = the offset
When measuring the dimension of your existing lock, 3 things are very important. And they are Functional Length, Cam Length and Mounting Hole. As the drawing shows, the Functional Length is Dimension A; the Cam Length, measured the cam from the center of the mounting hole to the end of the cam. If the cam needs to have an offset back or front to securely fasten the door, measure the offset like Dimension C. Last, the Mounting Hole should be measured like the picture shows.