Cross bars or Harness bars are bars which attatch from B Pillar to B Pillar behind the front seats. The are an attatchment for racing harness shoulder belts and also may stiffen the chassis somewhat.
They DO NOT offer roll over protection.
They can be dangerous to the driver in a crash if improperly installed or cheaply made. There are no regs that govern them.
My recommendation is the Brey Krause bar. See:
This bar attatches to the B Pillar using the factory mounting points and grade 8 hardware. You can retain the stock shoulder harness as well. It has shoulder harness strap guides to hold the belts in place from lateral movement. It has a reinforcing bar. It is wxcellent for a camera mount. It is a 4 point system with 2 down tubes to prevent the bar from submarining and add more chassis stiffeness. BK also manufactures Lap belt mounts which also retain the stock belts and allow you to clip in and clip out the racing belts and can accomadate a 6 point harness belt which is required for the stock seats. It is easily converted to a 5 point system if a racing seat is installed. BK also makes a nice Fire Extinguisher mount that mounts to the front seat rails.