Stock J-45 strings.
Masterbuilt 80/20 Lights are the stock/OEM strings that Gibson puts on every J-45 series and Hummingbird at the factory in Bozeman, Montana. When you purchase a new J-45, J-15, etc.. you get an extra set of these and Gibson custom service confirmed these have been the OEM strings for many years now. If you've purchased a Gibson Dreadnought used and you're trying to find strings to give you that tone and feel of what the new showroom models have, these are the strings you're looking for. That said, D'Addario produces the same product at a cheaper price. Search this site for D'Addario EJ11 80/20. I also recommend trying Elixir 80/20 Lights as all three of the string products listed have the exact same measurements/weights. Avoid using Light gauge Martin strings on a Gibson.They are weighted differently