People often ask how thick to make the headstocks on their cigar box guitars. Most standard guitar tuners, whether sealed-gear or open-gear, are intended to be used on a headstock that is about 9/16” (0.5625 inches/14.3mm) thick. Ukulele tuners are made to work on thinner headstocks, usually in the range of ⅜” (0.375 inches/9.53mm) or 7/16” (0.4375 inches/11.1mm).