Mr Devin sent me a rulebook when I was a race official yrs ago in their it stated openings on R/S had to be so big, don't know if it's changed since then. I see some of these sprint cars where the R/S opening is very small & w/ these containment seats I hope drivers can get out quickly of theirs a fire. I never saw a rule book so complete b4 in my life as that USAC book was