Mediums for my straight guitar that are tuned down a full step and lights for my Nobro cuz they're tuned way up to open G in an E form which put a lot of tension on them. I swap out the wound G string in the light set for an unwound G usually about a 19-20 guage. The tension level will cause the wound G string to break easily. I used to use a custom heavy guage set of strings on my Nobro and tune down to open C or even Bb. But it was costing me a fortune in strings because I was adapting a bass string for my low string. The cost of the bass string alone was around five bucks! It became a real challenge to tune at such a low pitch and it seemed that the strings quickly became dull sounding.