jackscrew
n. a threaded rod used for centering and balancing a vault door & frame in position during installation

jamb
n. the vertical components of a door frame

jiggered finish
n. a surface adorned with overlapping concentric circles

jimmy proof
adj. pertaining to a lock having a bolt which interlocks with its strike

JIS
abb. Japanese Industrial Standard

jumbo cylinder
n. a rim or mortise cylinder of 1-1/2" diameter