9.3.39. SCATTERSHIELDS/CHAIN GUARDS
The installation of scattershields or explosion-proof bell housings shall be required on all cars (except Showroom Stock, Spec Miata, Touring and Improved Touring) where the failure of the clutch or flywheel could create a hazard to the driver. Chain drive cars shall be fitted with a protective case/shield to retain the chain in case of failure.
Minimum material specifications are:
.125 inch SAE 4130 alloy steel
.250 inch mild steel plate
.250 inch aluminum alloy
NHRA or SFI approved flexible shields.
After reading the above, I wonder if the material specifications have been in place for a while (back when the rule was for scattershields only). Do you think they meant that chain guards have to be that thick and strong? I can only remember seeing one car that had a chain guard that would fit those material specifications.