and Double Cylinder each has it's own application.
Single cylinder is the most common, use it when you have a door without a big window. Key operation is outside only
Double Cylinder is mainly used when the door your are installing it in has a window, you wouldn't want someone to break the window and just open the lock. So both sides need a key to be operated. Be sure to keep the key out of the lock and out of reach of an intruder.
Remove the old dead bolt by centering the handle and unscrewing both screws all the way out and removing them.
Next remove the two screws holding in the dead bolt shaft and push the shaft from the inside and pull out and discard
Tools you will need
Phillips head screwdriver, Flat head screwdriver, or cordless drill,
Pencil,1/2 inch wood Chisel
Install the new shaft by pushing it into the existing hole
all the way, attach it using the screws
Now when installing the front plate the shaft must go through the slot in the shaft, see above pic
While holding the front with one hand, take the back cover and align the shaft in the slot in the rear cover plate. You will have to rotate the handle up so once in place you can insert the two long screws into the deadbolt.
Once you have aligned the cover plate into place, insert the two screws into the holes and start them by hand. When you know they are properly aligned, screw them down tight with the screw driver or cordless, do not over tighten.
Check for easy operation, if not easy, try easing up on the screws a little, you may have them to tight.
To properly align strike, let dead bolt shaft out and close door only enough to allow shaft to lightly touch frame or trim. Use a pencil to mark the location and open door. Align strike making sure it is centered with the pencil marks and screw down tightly.
Check operation of deadbolt and make sure you check that the key works properly
Your done, Congratulations. Or do you have to install the new Lock set? If so, go next page..