Constructed from proprietary Fox super light steel (SLS). Unique surface treatment and stress relief process allows using a smaller wire diameter with fewer coils, all creating a lighter spring . 1.385″ inside diameter fits Fox coil shocks, plus Marzocchi, DVO, MRP, X-Fusion and more . Spring fitment help https://tech.ridefox.com/bike/general-info/918/all-sls-and-standard-steel-rear-shock-spring-information