There Are Two Types of Garage Door Springs:

Extension: These springs lift the door with a cable and pulley system.  They travel along the horizontal tracks of your garage door and are mounted to an eye bolt on the doors structural back hang.  Extension springs are nearly at rest when the door is full open and fully extended when the door is closed.  Not all extension springs will work for your door.  Each door takes a specific pair of extension springs for optimal and safe operation.  If the wrong springs are applied, the door may not lift with ease or could possibly cause injury from too much tension.  There is an industry standard for extension springs in which one or both of the ends are color coded appropriate to amount of pull or lifting strength.  If you are not entirely sure of the color or weight of the door it is in the best interest of your safety to call a professional garage door installer and repair company in NH.  The extension springs have a cable that runs through the spring referred to as a safety cable.  If the spring ever fails it will not cause human injury or property damage because the spring is contained on this cable.  This a very safe operating system, however, unlike torsion cables, extension cables are much longer and much more exposed to a person or property in the immediate vicinity if they were to fail.

Torsion:  These springs are mounted on the top of the door fastened to the header and mounted through 3 bearing plates with a tube shaft running through the center.  On typical single car garage doors there is 1 spring and often with double car doors (16 or 18’ wide) there are two springs.  These springs assist lifting the door with a torquing motion once the springs are wound and secured.  The cable and pulley system to lift the door with this system are a series of two drums (which act like the door’s transmission) and 2 cables.  These springs receive there tension by using an appropriately sized and tight fitting winding bar to wind the springs.  Torsion springs should only be replaced or installed by a professional garage door company in NH.  Specific tools are needed to tension these springs and while they are wound are under a tremendous amount of tension.  These offer the safest and smoothest lifting system and are typically installed when there is enough head room to allow.  If a spring ever fails it remains on the tube shaft and the risk is reduced from any flying debris.  The cables are also in a better spot so as to not go whipping across your garage possibly injuring a person or causing property damage.  Life expectancy on a standard set of torsion springs in 10,000 cycles of your garage door.  High cycle springs are also available for additional cost that has a life expectancy of between 15,000 and 25,000 cycles of your garage door.

Also see: How to Replace Garage Door Springs