The following terms define Building and Machine Parts
jack: brace, support.
jack rafter: shorter-than-common rafter.
jamb: side frame of door or window in wall.
jib: projecting crane arm.
joggle: joint formed between notch cut in one surface and projection made in another, usually in wood or stone.
joint: point of contact between elements, usually held by glue, nail, or screw.
joist: horizontal support beam for floor or ceiling.
journal: portion of shaft or axle contained by bearing.