TIL: The hole on the back of a tuner is for lubrication. : r Guitar Don't Replace Your Strings Restore Them. Every time you play, your strings collect sweat, oil, and buildup that slowly kills your sound. Big Bends GEM TONE String Wipes bring them back MusicNomad TUNE IT Lube for Nut, Saddle, Bridge, String Guides FU Tone Gotoh Classical Guitar Tuners, With ivoroid knobs So I have a fender, an epiphone, and a Yamaha. All with vintage tuners. What's the best lubricant for these tuners? They're all perfect; and don't need to be changed, althoughI have Tuner lubricant? : r Luthier