The straps go through the door frames, and attach the rack on top of the roof, it fits almost all four door car without side rails, it fit four door car with side rails which height is less than 6.4 cm from roof, because the distance from car roof to bottom of bar is 6.5 cm. It can not be installed on two door car, because there is too small room between the two bars in two door cars. For sliding door, if the fixation of sliding door is not upper fixation, it will fit, because the tie down will go through the car. Comes with a pair of crossbars 48". Heavy duty steel tube make it strong and safe. Crossbars are adjustable in position. Install in minutes and disassemble in seconds. With water proof ratchet tie down. *DO NOT OVER TIGHTEN!* 1800 lbs ratchet tie down ensures the roof bar will remain firmly on your car top. Whether it’s a kayak, mountain bike, or ladder, these cross bars will get your favorite things to anywhere.