The PT-6700-00 is a great option to replace or upgrade the nut on your seven string acoustic or electric guitar. It was specifically designed for Carvin guitars. It has a flat bottom and is pre-slotted for a quick and simple install. Black TUSQ XL is engineered from the same material as TUSQ and is impregnated with PTFE which is five times more slippery than graphite. It has all the tonal benefits of TUSQ, bringing out the hidden harmonics of your guitar all while drastically improving tuning performance. Black TUSQ XL is consistent from piece to piece, and within each piece, to offer you harmonically rich tones without the problems associated with natural materials.