Today in welding class I found a welding rod laying in my booth. The number on it was 4055 and it said "crack resistant for cast iron welding AC or DCEP" I took it home to try on my AC welder and just running a bead on an old chevy steering arm, it seems like on 105 amps it wasnt burning hot enough, but seemed alot like a 7018. It was an 1/8" rod. Anyone know what the numbers on this mean? i know the 40 means 40,000 tensile stregnth. but the 55 at the end confuses me. Ive never heard of a 5 for a position number.