Mckay 309/309L Sterling AP description: A lower carbon version of the 309(H) Sterling AP. Low carbon content makes it excellent for applications where reduced susceptibility to sensitization during high temperature service is necessary. Outstanding for dissimilar metal welding such as weld overlay or for welding type 309 stainless steel to mild or low alloy steels. It has a smooth running arc that results in a uniform weld bead that is flat to slightly convex.