Unbleached cow bone nut. Grooves are cut with a string spacing of approximately 7mm to accommodate the 13, 15, 19, 28, 38, and 56 gauge strings, which Stevie Ray Vaughan is said to have used. (There are various theories regarding the specific gauges, which may vary depending on the time period, etc.) The bottom surface is straight. Since there is extra height, please shave it down to fit your guitar. Oil treatment before shipping is also available. #gibson #fender #PRS #Epiphone #zemaitis #ESP #Gretsch #Rickenbacker #Suhr #tokai #Fernandes #Fujigen #Greco #electricguitar #guitarparts #guitarrepair #guitarcraft #Stratocaster #StevieRayVaughan