GraphTech Black TUSQ XL String Tree Graphtech Black Tusq Xl Nut Sleek String Trees Designed to boost guitar performance, TUSQ XL is precision engineered and specially formulated to bring out the hidden harmonics and richness in every note. TUSQ XL is based on the highly resonant TUSQ man made ivory and impregnated with PTFE, the slipperiest substance on earth, to improve the tuning performance of the guitar. Improved tuning stability, improved harmonic content