[intocarss]

The NHRA requires all cars that run 13.99 or faster to have a drive shaft safety loop that meets general regulation number 2:4.



NHRA general regulation number 2:4.

Here is the complete specification word for word.

2.4 DRIVELINE

On any car in which the driver sits over or in back of the rearend center section, a suitable protective shield of .120-inch (3 mm) minimum thickness steel plate must be installed for those units with universal joints securely mounted to the rearend center section and the bellhousing adapter. Where possible, couplers are recommended in place of U-joints. For straight couplers, the minimum requirement is .063-inch (1.6 mm) aluminum which must contain an inspection cover for removal and inspection of the coupler, securely mounted to the rearend center section and the bellhousing adapter, or as noted in Class Requirements. In place of a crossmember, in the vicinity of the front universal joint, all cars in competition using open driveshafts, must have a retainer loop 360-degrees of enclosure, 1/4-inch (6.35 mm) minimum thickness and 2-inches (5.1 cm) wide, or 7/8-inch (22.2 mm) x .065-inch (1.65 mm) welded steel tubing, securely mounted and located within 6-inches (15.2 cm) of the front universal joint for support of the driveshaft in event of U-joint failure. Recommended the loop be round rather than oblong to minimize loading on loop. Open drivelines passing any part of the driver's body must be completely enclosed in 1/8-inch (3.2 mm) minimum thickness steel plate, securely mounted to the frame or frame structure.




20.10 Section 20 - General Regulations
ACCEPTED
DRIVELINE LOOP

mounted to the rear-end center section and the bellhousing
adapter, or as noted in Class Requirements. In place of a
crossmember, in the vicinity of the front universal joint, all cars in
competition using open driveshafts must have a retainer loop 360
degrees of enclosure, 1/4-inch minimum thickness and 2 inches
wide, or 7/8-inch x .065-inch welded steel tubing, securely mounted
and located within 6 inches of the front universal joint for support of
the driveshaft in event of U-joint failure. Open drivelines passing
any part of the driver’s body must be completely enclosed in 1/8-
inch minimum thickness steel plate, securely mounted to the frame
or frame structure. Driveshaft loop required on all cars running
13.99 (*8.59) or quicker and utilizing slicks; except vehicles running
11.49 (*7.35) seconds or slower equipped with street tires.