Under the CDL tank vehicle rules, what individual tank capacity triggers the need for a tank endorsement on a Class A or Class B vehicle?

AAMVA CDL Manual, Section 8 (Tank Vehicles), p. 8-8-1; consistent with the 'tank vehicle' definition at 49 CFR 383.5

This threshold determines whether a driver legally needs a tank endorsement before hauling liquids or gases in bulk. Getting it wrong can mean driving without a required endorsement, even if the cargo itself is not hazardous. Knowing both the individual tank size and the aggregate capacity rule prevents a driver from assuming small or split tanks are automatically exempt.