According to 2005 NHRA rulebook, 6" square by 1/8" thick, on top and bottom of floor, securely bolted together with atleast 4, 3/8" bolts, or top plate weded to rocker sill, with plates welded completely . Found under Section 16 - General Regulations 4:10 Roll Bars, Page 215 Shouldbe good to go!!! My 2006 rulebook is at home.