The 13mm sway bar is a great upgrade for improving the handling of the sled The larger diameter sway bar will reduce inside ski lift while cornering which in turn eliminates the "tippy" feeling riders encounter while cornering. The stock sway bars started at 10mm when the RX-1 came out. Yamaha later upgraded to 11mm in 06 on the apex. Currently the Apex and Vector sleds are coming with 11.9mm sway bars. The 13mm sway bar is a direct interchange with the stock bar on all sleds but the 03 RX-1. The 03 RX 1 & 05 Rage had a smaller spline diameter, so you will need to upgrade to 04+ link arms to utilize the 13mm sway bar. I will include used ones at no charge. You can select this option when you check out in the store.