Enables the Thule cargo box to ride just perfectly. unless you have the ball/socket locknut completely tight, the socket will freely and easily pull off of the ball mount. But not in others. its just like it is in the picture,a lil snug but not uncomfortable , fits good ??,so to help anyone out Im 52 , 214lbs?? & i ordered the xl glad i did cause the large wouldnt have fitted. It dries so fast (really within 10s! 5Great shoe though. Also they run small. How do I determine that?I won?t be using this rack very often so it is probably okay. I dont think it would take turning the volume up as loud as a standard boombox but it does just fine at what I would call a loud volume. The wires where you put your wine bottles are poorly welded onto the metal.