I used the light tan looking pellets they come like 6 to a package, i think they are partly made with crushed walnut shells, anyway they were recomended buy a few folks to stop my rather large leak of coolant out of two exh studs on a 383. They worked great i only used 4 of the six pellets, i was also told GM used these from the factory on some of their problem engines (northstar ect. )