Hello Ben, apparently the stuff comes in two 'flavors', that being Yellow and Green. The yellow appears to be formulated for the softer metal alloys such as brass, allie, copper etc. The green label is a bit more course and is better suited for steels, cast iron, stainless and the like. The kind that you purchase would seem to depend upon what materials you will be consistently using it on. I'm guessing here that the yellow label *could* be used on steels but would merely take longer to get the desired results, don't know for certain. Perhaps a tele call or an email inquiry to the manufacturer or distributor would help in your decision making.
BC1
Jim