NHRA 4:10 says cars without a frame must have roll bar secured by 1/8 inch thick 6"X 6" plates on both sides of the floor secured with at least 4 3/8 bolts.
There is some incorrect information in this thread. If installing a cage per nhra( not a roll bar) those plates have to be fully welded to the floor. Bolted plates only allowed for a bar.
Also there is no height requirement for the hoop. The NHRA rule book states that the drivers head must be 3 inches below the height of the hoop when sitting in the seat. The height of the seat and driver are variables for compliance with the rule.
