These are Thomastik contrabass strings, specifically the 3rd and 4th strings. They came on a contrabass I received, and based on the ball-end colors and what the previous owner told me, I believe they are Belcanto Solo strings. I used them on a full-size contrabass. They were used for over a year (I don't know how long the previous owner had them on). I used them for solo playing in standard tuning. Both the previous owner and I only used them for jazz, and we never played arco, so there are no rosin marks, and they are in relatively good condition. After use, I wiped off any skin oils and regularly maintained them with String Life. Therefore, the surface is still quite shiny. However, since they were used normally, there are some creases and coil memory. I replaced them this time because I felt the sustain had decreased. They are still in usable condition, so I'd like to offer them to someone who wants to try them. Compared to the new Spirocore strings I put on, they have a warmer and gentler tone. Since they are the lower strings, they might be easier to introduce. Please note that I cannot track these strings by serial number, so returns are not accepted.