The PT-M169-00 is a great option to replace and upgrade the nut on your Martin Style guitar and other guitars with similar specifications. This nut is slotted. Black TUSQ XL is designed to boost guitar tone and performance. This precision engineered nut is made with a specially formulated material which couples the strings' vibrations to the neck and brings out the hidden harmonics and richness in every note. It is based on the highly resonant TUSQ man made ivory, but is impregnated with PTFE to improve the tuning performance of the guitar.