Martin 28-43 Classical Ball End Hard

The "28-43" refers to the gauge or thickness of the strings, with the first string being 0.028 inches in diameter and the sixth string being 0.043 inches in diameter. "Classical" refers to the type of guitar the strings are designed for, which typically has a wider neck and a different playing style compared to a steel-string acoustic guitar. "Ball End" refers to the shape of the end of the string, which is designed to be used with guitars that have a tailpiece or bridge that requires ball-end strings. Finally, "Hard" refers to the tension or feel of the strings, with hard tension strings providing a greater resistance to bending and a more powerful tone compared to medium or low tension strings.