These springs slide over the shaft, inside the larger outer springs to create a truly progressive rate effect when engaged.  Rates available 200, 300, 400, 500.   NOTE: 500# inner springs will not fit over .625 or larger shafts.
     Made for use with our standard style cups and retainers with 2.5" outer springs - not recommended for use with our offset cups and offset retainers unless you are using the longer 3.0 outer springs.