The Kwikset Locking Bar Spring is designed to be used on most 6-pin Kwikset Signature Series Pin and Tumbler Keyed entry knobs and the 780/785 6-pin series deadbolts. This spring is what holds the locking bar in the cylinder housing. These are factory original locking bar springs.  This locking bar spring is what holds the locking bar in most Signature Series knobs and the deadbolt locking bar on the 780/785 Series deadbolts which use the 6-pin Pin and Tumbler cylinder. This spring along with a locking bar is what allows the control key to remove the cylinder without taking the lock off of the door. This is a great feature for rotating the knob cylinder 180 degrees for proper key positioning or for jobs where rekeying is done frequently. Normally, you do not replace the locking bar spring unless it gets damaged during the re-keying process. Smart Key Cylinders do not use this locking bar spring.