Cigar Box Guitar Tool - Nut and Bridge File for String Grooves These repurposed long-shaft welder tip cleaners are good for filing string grooves in nuts and bridges Recommended for bone, wood and soft metals. Use gently for best results Perfect for cigar box guitars and other homemade instruments Files range from .015" (.38mm) up through .0615" (1.54mm) These longer-shaft files are easier to use than the shorter ones commonly available at home improvement stores