I'm assuming you mean the cross bars? I haven't had any problems with my OEM crossbars, they're spaced about 26 inches apart, from front to back, and should fit your normal 3 ft metal dog crate no problem. The only problem I foresee would be that they're "rounded" and the dog crate might not lay completely flat on them. Shouldn't be a huge problem, but some of the aftermarket crossbars seem to be more flat, or maybe they're just thicker.
See pic for reference of what I'm talking about, hope it helps.
See pic for reference of what I'm talking about, hope it helps.