Running  Boxster Spec or SPB and don't want to hassle with "other" brands and their NON-Compatibility with the PSS9's? Want to use the number one spring in NASCAR? Tarett Engineering brings you SWIFT racing springs!! These springs are physically lighter than anything on the market and are sold in METRIC sizes! (Bilstein utilizes metric springs) This "kit" supplies you with the class legal 450-500 rates you need to be legal. These are a DIRECT REPLACEMENT for the PSS9 springs, 100% compatibility. No machining of hats or spacers required, no loss of shock travel!!