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