Nova extreme pro, setup info?

i went with the 48 inch nova pro and i have some questions. the mounting legs are wider than the fixture, is there a way to secure them so they won't slide back out now that they are adjusted to fit the tank? also, the package came with four little black rubber knobs, what are these for? the only thing i can think of is to keep the legs on the rim of the stand, but i wanted to know for sure. thanks
The rubber bushing is used only when your not using the tank risers.You place them on the bottom so the light doesn't actually touch the tank except on those rubber bushings.

The weight of the light was enough to keep the legs from slipping.If you have young kids then you may have to secure it.I can't think of anything but tape.