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Glossary of Spring Terms

Below are some common terms used when referring to units of measure and and other features of spring manufacturing and use.

AC Active coils. TC – 2 (in most cases)
Close Ends The end of the wire coil on a compression spring where it touches the next coil.
Closed and Ground Ends Where the end of the wire coil touches the next coil and is ground flat so as to sit flat on a compression spring.
Compression Spring An open-coiled spring that offers resistance when compressed.
Extension Spring A spring that absorbs and stores energy while offering resistance to being pulled.
FL Length of a compression spring.
Hydrogen Embrittlement Occurs during the process of plating the spring and may cause it to fail.
ID Inside diameter. OD – (2 x wire size)
Initial Tension Force that holds the coils tightly together.
Inside Hook Length Length from the inside of the hooks or loops.
Load Force applied to a spring that enables it to move.
OAL Length of an extension spring from end to end.
OD Outside diameter. ID + (2 x wire size)
Pitch Distance from the center of one wire to the center of the next wire.
Plain End Where the pitch remains the same throughout the spring including the end coils on a compression spring.
Solid Height Height of a spring when fully compressed.
Spring Index The ratio of coil diameter to wire diameter.
Spring Rate Amount of lbs it takes a spring to move 1 inch.
Stress Relieve Heating a spring at a lower temperature to remove stress from coiling.
TC Total number of coils in a spring.
Torsion Spring A spring that is rotated offering resistance to externally applied torque. Ends can vary in length and be bent.