Cello nut grooves - approx one third the diam of the string deep. C string 0.75mm clearance between string and board.
A string 0.5mm. The final clearance can be measured once strung up with shims of plastic sheet. The height of the nut prior to cutting the grooves
can be set by adding the clearance to the 1/3rd diam. - ie Spirocore C is 1.7mm diam, so 0.6mm + 0.75mm = 1.35mm above
the board.