1971 NASCAR International Stock Car Racing Rule Book NASCAR Grand National Championship Division Section 20-12 -- Drive Shaft

a. Drive shaft and universals must be similar in design to standard production type.

b. It is mandatory that two U-shaped bracket, no less than 2 inches wide and 1/4 inch thick, be placed around the drivehsaft and fastened to the floor or cross member of car to prevent driveshaft from becoming dislodged and dropping to race track.