They have to be hung on a wall or flat surface. They are pretty solid, my friend has one and it works really well if you have lots of different things to hang, like snowboards, skateboards and such. The WakeWorx racks are really just for wakeboards and wakeskates but because the backs are flat they can be screwed onto anything flat. I have a pair and a speaker box in the back of my Expedition for board storage. They can also be screwed to the back of truck beds for storage or on any wall or flat place. That is, of course, in addition to the universal fit to towers and such.