top nut, unbleached bone, 43,5x8,5x5,5mm, pre-filed, spacing 35,2 mm This nut is made from unbleached bone, a long-time favourite of many luthiers. The slightly self-lubricating properties of unbleached bone as opposed to the very white bleached bone are a good reason to use this nut material. When polished, the looks of unbleached bone are very elegant and will add class to your guitar.