LOOSE STRING FOR CLASSIC GUITAR Spanish guitar string D'Addario T4501 Titanium series. Caliber .041 ''. Crafted from a dense monofilament material that has an attractive, translucent purple hue. The T2 strings have a polished feel, similar to nylon string, but with a slightly brighter tone and greater projection. As a result, you can replace titanium treble T2 strings with nylon strings with very little acclimatization to shifting.