On Sunday, September 21, 2014 6:15:37 PM UTC-5, wrote:
If you have some means of measuring the diameter of the wire used to make the coil spring, that along with the number of turns on the coil itself should allow you to get the correct replacement. Good idea to replace after 25 years or more life. When you put in the new springs, I highly recommend the use of a cable running down the middle of the spring that is tethered to something substantial to prevent the spring pieces from doing serious damage if it should break at some time in the future. The internet has lots of views under garage door spring safety.

Good points here...but also measure the diameter of the coil. In my experience these springs break at the end loops...I've taken the old loop and run it into the spring and held it with a cable clamp (to keep it from sliding off). It is only a slight overstretch...and I haven't had any come off. (use at your own discretion)