U

upper pins
The pins in a lock that sit on top of the lower pins.

uncontrolled cross keying
n. a condition in which two or more different keys under different higher level keys operate one cylinder by design; e.g., XAA1 operated by AB, AB1 NOTE: This condition severely limits the security of the cylinder and the maximum expansion of the system, and often leads to key interchange

uncombinated
1. adj. of or pertaining to a cylinder which is or is to be supplied without keys, tumblers and springs 2. of or pertaining to a lock, cylinder or key in which the combination has not been set

unassociated master key
n. a master key which does not have change keys related to its combination through the use of constant cuts

unassociated change key
n. a change key which is not related directly to a particular master key through the use of certain constant cuts

UL
abb. Underwriters Laboratories