I honestly just use cheap plastic drywall anchors. Electricians would call them reds and threads or blues and screws... either way, these work fine. I have a maxspect 4' led bar that is pretty heavy hanging from two anchor points. My wife even puts heavy ceramic Christmas decorations on my light bar. Never an issue. I would never think that you would need such a overkill weight rating to build a cross brace between joists.