Like the title says, does anyone know what kind of material and size/thickness of material the harness bars are made of? Also, how strong do the mounting points have to be? I only plan on using it for autocross so it wont see any major forces like it would if I were in an accident.

I was thinking about making one but don't want to build something and then find out it is too weak to be useful. Would the latches by the rear seats be strong enough to mount the harness bar to? The inside diameter has to be 18.3mm/0.7205in/or 23/32in (All those measurements are the same size) or slightly smaller.

Thanks,
Mike
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Would 0.120 DOM tubing work?
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Now.....I'm gonna assume you need to conform to SCCA specs & rules....

The size of tubing to be used shall be determined on the
basis of the weight and speed potential of the car. The following
minimum sizes are required required and are based
upon the weight of the car without the driver.
a) Over 1500 lbs.-min. of 1-1/” 2 o.d. x .120" wall or 1-3/4"
o.d. x .095" wall
b) Over 1000 lbs.-min. of 1-1/4" o.d. x .090" wall
c) Under 1000 lbs.-min. of 1" o.d. x .060" wall
Dimensions are nominal. 0.005” variation in wall thickness is
allowed.

Along with that...
Each mounting plate shall be at least .080" thick if welded and
3/16" thick if bolted. A minimum of 3 bolts per plate is required
for bolted mounting plates.
All bolts and nuts shall be SAE Grade 5 or better, 5/16"
minimum diameter.