As of July 2015, Lowes.com sells 11 Blue Hawk and Genie brand garage door extension springs ranging in prince from $15 to $20. The springs are steel, 27.5 or 27.95 inches long, and have weight ratings ranging from 90 pounds to 140 pounds.
The extension springs Lowe.com offers, which are all for residential garage doors, all come with safety cables. Extension spring tips are color-coded according to industry standards to indicate their weight ratings. Many of the springs on Lowes.com list a color, as well as a weight rating, so someone replacing old springs who doesn't know the weight of the garage door can match the color to get the correct new springs.