CID A-A-59452B covers flexible metal hose. Class 1 metal
hose is intended for use as air ducts or speaking tubes and other applications requiring
flexible hose but not for the conveyance of liquids. Class 2 metal hose is intended for use
with carburetor preheating systems, exhaust connections, and other applications requiring
flexible metal hose with heat-resistant properties up to 1200°F.