Darrell Day, In the 1929-53 Chevy Master Parts Catalog they are listed under Parts Group# 8.866 - Connections, Hot Water Heater.

More specifically listed under that Parts Group as: Nipple, heater coupling (3/8) GM# 3106066

Chev's of the 40's carries a reproduction piece under Heater Hose Nipple with the same ID number as the original GM part number.

~ Dan
1951 Chevy 3 window 3100
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"My Grandpa Carl's Truck and How it Became Mine"
1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver)
US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)