Duramax LLY/LBZ Head gasket set with head bolts - types "B or C" 6.6 silverado diesel 2004-2007 .0394 thick type "B or C" Vins "2 or D" LBZ or LLY GM Duramax Diesel Engines. Fireseal gaskets by Enginetech The .0394 gaskets meet the GM specifications for the "B" and "C" head gaskets - due to overlapping specs. These gaskets are right in the sweet spot.