I use Martin mediums for D G B E but I use D'Addario heavies for my bass E and A on my Martin K2. Since I run a very heavy bass rythmn, and the koa wood sings in the bass, plus the "Martin Sound", it's where I want to be. Though Martins state only "medium or less", if you look at the string tension charts, the poundage is almost the same. I've done this for years, with no damage to the top and a MUCH better sound. I think the package number is 118, and I've ordered them in bulk for years though they now only make them in sets. And if you ever go to Dropped D, you will not leave home without them.