Sperzel's rear thumbscrew locks the string; ideal for tremolo guitars. String posts have graduated heights (perfect for that strat or strat style guitar) and the tuners feature a 12:1 ratio, sealed lubrication, metal knobs and threaded peghead bushings. Single pin mount keeps tuner from rotating, no mounting screws needed. For 9/16" - 11/16" thick pegheads, requires 10mm (13/32")-diameter pegholes. Sold in sets of 6.