force from the spring, whatever the position of the boom. This creates a horizontal "pendulum" with very long oscillation period. Long-period pendulums enable seismometers to sense the slowest waves from earthquakes. The LaCoste suspension with zero-length springs is also used in gravimeters because it is very sensitive to changes in gravity. Springs for closing doors are often made to have roughly zero length, so that they exert force even when the door is almost closed, so they can hold it closed firmly. Uses Airsoft gun Aerospace Buckling spring keyboards Educational Firearms Forward or aft spring, a method of mooring a vessel to a shore fixture Industrial Equipment Jewelry: Clasp mechanisms. Lock mechanisms: Key-recognition and for coordinating the movements of various parts of the lock. Spring mattresses Medical Devices Mini Drill Pens Pogo Stick Pop-open devices: CD players, Tape recorders, Toasters, etc. Reverberation in electronic organs Slinky Spring reverb Spring shoes Switchblades: Folding or sliding knives with a spring-loaded opening mechanism. Toy Trampoline Upholstery: Upholstery coil springs Vehicles: Vehicle suspension, Leaf springs Watches: Balance springs and in mechanical timepieces, mainsprings for winding mechanical timepieces, and spring-loaded bars for attaching the bands and the clasps. See also Shock absorber Slinky, helical spring toy Volute spring References Further reading Sclater, Neil. (2011). "Spring and screw devices and mechanisms." Mechanisms and Mechanical Devices Sourcebook. 5th ed. New York: McGraw Hill. pp. 279–299. . Drawings and designs of various spring and screw mechanisms. Parmley, Robert. (2000). "Section 16: Springs." Illustrated Sourcebook of Mechanical Components. New York: McGraw Hill. Drawings, designs and discussion of various springs and spring mechanisms. Warden, Tim. (2021). “Bundy 2 Alto Saxophone.” This saxophone is known for having the strongest tensioned needle springs in existence. External links Springs with Dynamically Variable Stiffness (patent) Smart Springs and their Combinations (patent)