This cart entry is for one PAIR of Swift 60mm ID x 60mm x 15 N/mm Tender Springs. This includes Swift's spring adapters along with their shims. These are high quality tender springs that are made in Japan.
Tender springs can be used in most coilover strut applications to help prevent unseating of the main spring from the perches at extreme droop (normally only when the car is jacked up for service). The tender helps keep a spring from potentially making an unwanted "klang" noise when it re-seats. Tender springs are optional on many of our AST coilover kits - please ask if you are unsure if they are needed for your application. Sometimes a tender spring can make the total spring package taller and potentially interfere with extremely wide wheels/tires (example: BMW front strut cars are an example where tenders are almost never used, due to wheel/tire clearance issues). Otherwise running a tender spring on a coilover package has no downsides.
Tender springs are wound with a flat coil wire that allows this type of spring to compress to "coil bind" without damage. These springs have a very low spring rate and, when used properly, should compress flat once the car is sitting at ride height - becoming nothing more than a spring spacer, until the strut extends to full droop. This means they do not affect your working spring rate. Once at extended droop lengths the tender spring extends and exerts its additional force against the suspension components, and keeps the main spring from rattling loose in its perches.
Most applications using a 60mm ID coilover springs work well with an 60mm or 80mm long tender spring with rates from 10 to 20 N/mm. 15 N/mm = 86 pounds/in, so the rate these offer is pretty low (you can step on a tender spring to compress it flat). Tender springs can sit above or below the main spring (there is no preference).