C.F. Martin Acoustic Guitar Six String Phosphor Bronze Bluegrass, .013 - .056, MSP-4250star rating 5BobDecember 16, 2009Nice clean crisp sound with these strings. I tried the Elixirs and D'Addario's but these really bring out that "Martin" sound for bluegrass. I get a lot of compliments on the sound at jams I attend. I've been using them for about 2 years now. I play daily and these last me a month in the winter and about 3 weeks in the summer. You can't beat the service of JustStrings either. It is painless, click add to cart and in a few days, they are in the mailbox. The price is good too. I am really pleased with both the Martin strings and JustStrings.