The most effecient way to carry multiple whitewater kayaks. Product replaces 520 Kayak Stacker. Four boat maximum capacity. Tying boats down is now easier than ever with the upper bridge design. Easy carrier transfer from vehicle to vehicle with proven universal hardware. For a clean look when not in use, The Stacker folds down flat. Includes one pair ratcheting tie downs, two straps and buckle protectors. Fits Thule bars, YakimaR bars, and most factory installed racks. May require the use of Xadapt3 80 MM bolts on some factory applications.Please consult your local retailer for further information. This item will require the use of Xadapt3 80 MM bolts on our XSporter 421422 and Rapid Aero Bars.