Where does it say that it needs to be steel? I'm seeing that it only needs to be steel if it's made of tubing. Am I misinterpreting?
You are correct, needs to be steel if it's made with tubing and this particular loop appears to be tubing.
DRIVESHAFT LOOP DEFINITION: 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 to the frame
or frame structure where available (or to the OEM floor or rocker
box where a frame does not exist) and located within 6 inches
of the front or rear universal joint for support of the driveshaft in
event of U-joint failure.
DRIVESHAFT TUBE DEFINITION: Driveshaft must be covered
by a 360-degree round, oval, or tapered tube, covering the front
U-joint and extending rearward a minimum 12 inches. Minimum
thickness of tube is .050-inch steel or titanium. Driveshaft tube
must utilize a minimum of four attachment points to the chassis,
using either minimum 5/16 SAE Grade 8 bolts, welded, or 1/4-
inch push/pull pins. Two-piece tube assembly permitted with a
minimum of six 3/8-inch SAE Grade 8 bolts.
