University of Iowa Libraries       Lichtenberger Engineering Library

Glossary of Bridge Terminology



Jack: A lifting apparatus. A mechanical device, appliance, or part of a machine. To pry up or lift; with a jack.

Jack Arch: An arch limited in thickness to that of one brick.

Jack-bores: The bores of a jack either on the inside or the outside.

Jack Chain: A small chain each link of which is formed of a single piece of wire bent into two loops resembling the figure eight.

Jack Engine: A small engine employed in sinking a shallow shaft, a donkey engine.

Jack-head Pump: A pump having its delivery pipe attached to the pump barrel by a goose-neck connection.

Jack-knife Bridge: A bridge in which the lifting arms fold on themselves at mid length when in a raised portion.

Jack Plane: A carpenter's tool for smoothing boards.

Jack Rafter: One of the short rafters used in a hip-roof.

Jack Rib: Same as "Jack Rafter."

Jack-roll: A windlass.

Jack Screw: Same as "Screw Jack." -- A large screw working in a nut set in a strong frame or forming a part thereof, which in turn serves as a base to carry the load.

Jack Shaft: In rolling-mill machinery, a shaft that takes the power from the engine shaft and transmits it by pinions and spindles to the rolls.

Jack Stringer, or Outside Stringer: A stringer placed outside the line of main stringers.

Jack Timber: A timber in a bay, which, on account of being intercepted by some other piece, is shorter than the rest.

Jacket: A covering placed around an object to prevent the escape of heat by radiation.

Jag Bolt: Same as "Barb Bolt." -- A bolt having jagged edges so as to prevent its being withdrawn from the object into which it is driven.

Jag Spike: Same as "Jag Bolt."

Jam Nut: Same as "Check Nut." -- An extra nut which is screwed on a bolt tight against the first nut to prevent the latter from working loose.

Jambs: The sides of an opening through a wall.

Jaw: Any part of a construction, which, from its position, shape or use, bears a resemblance to the jaw of an animal.

Jaw Clutch: A clutch composed of two hub-like castings having jaws that engage each other. One hub is arranged to slide on its shaft as well as to rotate with it, so that it can be thrown in or out of gear.

Jaw Coupling: Same as "Claw Coupling." -- A coupling in which the claws of one part fit into the recesses of the other part with a little amount of play; so that when the shafts are out of line, the coupling will accommodate itself to the obliquity without overstressing the shafts.

Jaw Plate: The unsupported portion of the end of a compression member remaining after the outstanding legs of flange angles have been cut away, and its pin plates, which extend below the transverse diaphragm to allow the packing of other members on the same pin.

Jemmy: A short crowbar. Also called "Jimmy."

Jet: A spouting or spurting, as of water or flame, from a small orifice.

Jet Chain: The chain which picks up a pipe that is used for the purpose of jetting.

Jet Condenser: Same as "Injection Condenser." -- A form of condenser in which the injected water comes in contact with the steam.

Jet Hose: A strong hose used for jetting purposes.

Jet Nozzle: The contracted and perforated portion at the bottom of a jet pipe.

Jet Pipe: A pipe used in jetting, having a nozzle at the lower end and the water supply hose at the upper.

Jet Pump: Any pump in which the fluid is impelled through the discharge pipe by the action of a jet of the same or another fluid.

Jetted Pile: Any pile that has been sunk by means of a jet.

Jetting: Putting down by means of a jet.

Jetty: A structure of wood, stone, or mattress extending into a body of water and serving for a wharf or pier, or as a mole, rampart, or wall. Also used to restrain, charge, or direct a current, and to protect a harbor, shore, channel or the, like.

Jetty Head: The projection at the end of a jetty.

Jib: The upper projecting member or arm of a crane supported by a stay.

Jib Crane: A crane having a swinging boom.

Jig: Any tool or fixture used to guide cutting tools.

Jig Saw: A reciprocating sawing machine having a narrow vertical blade set in a frame which has an oscillating motion.

Jigger: A small, light, or light-running mechanical contrivance, causing when in use a rapid, jerky motion. Any subordinate mechanical contrivance to which no more definite name is attached. A warehouse crane.

Jigger Pump: A portable, hand-lever pump, usually provided with an attachment for an air chamber and a nozzle to which a hose may be attached.

Jim-crow: An implement for bending or straightening rails.

Jimmy: Same as "Jemmy."

Jimmy-wink: Any short, light, stationary derrick used for raising small loads.

Job: A particular piece of work. Any undertaking.

Job Work: Work done by the job.

Jockey Pulley: A small wheel running against the rim of a grooved wheel to keep the rope or chain in its groove.

Jockey Wheel: A small wheel running against the rim of a grooved wheel to keep a rope, wire, or cable in the groove.

Joggle: A stub tenon on the end of a post or piece of timber, which prevents it from moving laterally.

Joggle Beam: A built-up beam having a joggle.

Joggle-piece: The upright member in the middle of a truss; a king post.

Joggle Post: A post built of two or more pieces of timber held together with dowels or joggles. A post having shoulders to receive the feet of struts; a king post.

Joggle Truss: A type of timber truss in which the members are connected by joggles. Also a truss having only one joint.

Joggle Wheel: A wheel which has a wabbling motion.

Joggle Work: Masonry construction in which the stones are internotched or keyed.

Joint: The place or part in which two things or portions of one thing are joined or united. The mechanism, method, or means by which such junction is effected.

Joint Bolt: A bolt joining one timber to another in a "T" form.

Joint Coupling: A form of universal joint in which the sections are coupled and locked together.

Joint-end: The iron end-piece about which another part moves as on a pivot.

Joint File: A small round file of uniform section throughout its length.

Joint Hinge or Strap Hinge: A hinge having long leaves joined at their large ends.

Joint of Rupture: That joint in a voussoir arch for which the tendency to open at the extrados is the greatest.

Joint Pipe: A short section of gas or steam pipe.

Jointer: A tool for filling the cracks between courses of stone in masonry. A long planer to straighten the edges of boards. A tool for heading a joint.

Joist: To fit or furnish with joists. One of the horizontal pieces usually laid in equidistant rows to which flooring is nailed.

Journal: That part of a shaft or axle which rests on the bearings.

Journal Bearing: The immediate support of an axle or a shaft.

Journal Box: A one-piece box or bearing for supporting a journal.

Journal Brass: One of the pieces, usually of brass, which fits up against the journal in a journal box.

Journal Friction: The resistance to rotation offered by the surface of the bearing to the revolving axle or journal.

Journal Packing: Waste, cotton, or other fibrous material saturated with oil or grease and placed in a journal box to lubricate the axle.

Jumbo: A term descriptive of anything which is unusually large. The cooler for the cinder notch of a blast furnace.

Jump: An abrupt rise in a level course of masonry.

Jump Joint: Same as "Butt Joint." -- A joint in which the ends of the pieces are square and press against each other.

Jump-up: See "Jumping."

Jump Weld: Same as "Butt Weld." -- A weld in which the pieces are butted against each other and then joined by welding.

Jumper: A dolly; a monkey. A spark from a ladle of molten cast iron.

Jumper Drill: A drill similar to a churn drill only much shorter.

Jumping: Upsetting a bar, etc., or increasing the cross section of same by striking it on end.

Junction Shaft: A spindle in a rolling mill.

Junk: Worn out and discarded material, machinery, structures, etc., that, in general, may be turned to some use; such as old iron or steel which may be remelted and again sold. Same as "Scrap."

Junk-dealer: One who buys junk.

Junk Iron: Same as "Scrap Iron."

Jut: To project out. To shove or butt. A projection.

Jute: The fibre of a plant grown in India, used for gunny sacks and packing.

Jute Packing: Packing made of jute fibres and put up in the form of a soft, loosely woven rope.

Jutty: A pier, mole, or jetty.