From the sound of it, it seems that you've combined the wheel and the table.
Does yours look something like this?

Cause if it's, it means what you got to do is to split it up with the Split Body tool (Model > Modify > Split Body).
Looking at your model, I guess you want to place the wheel at each foot of the table? In that case I recommend you to make the wheel into a component (left click body > right click > create components from bodies) to prevent it from merging and this will allow you to have multiple instances of the component (updating one will reflect changes in the other same components)

Do remember that when it body mode, if you have more then 1 body (eg: Body 1 and Body 2), if Body 1 touches Body 2 with any command, it'll auto merge both bodies, to prevent that you can either turn off Body 2 when Body 1 intersects or if you forget, you can use the split body tool to split it back (in some situations it'll get messy so might as well make it into a habit to turn off other intersecting bodies if you don't want it to merge)
Omar Tan
Malaysia
Mac Pro (Late 2013) | 3.7 GHz Quad-Core Intel Xeon E5 | 12GB 1.8 GHz DDR3 ECC | Dual 2GB AMD FirePro D300
MacBook Pro 15" (Late 2016) | 2.6 GHz Quad-Core Intel Core i7 | 16GB 2.1 GHz LPDDR3 | 4GB AMD RadeonPro 460
macOS Sierra, Windows 10
