21:1 Tuning Ratio; Makes for a finer degree of control than lower ratios; The locking part makes it easy to keep the guitar in tune due to less winds on the post, no slipping, and allow for quick change time and effort if a string breaksEasy to install and convenient to use, insert the string through the post hole, wrap around once, then lock by tightening with the thumb screwPrevent slippage and help eliminate out of tune frequency, provide a smooth and precise tuning experience that will keep your guitar in tune for longer periods. The locking mechanism ensures that the strings remain secure and tight, preventing any unintentional slipsLocking tuners are excellent for non-locking tremolo guitars, and for players that do heavy string-bending. Tuners and all mounting hardware packed well in a foam boxprecision locking tuners for most 3 per side electric/acoustic guitars with modern 13/32"(10mm) tuner holes and 90 degree mounting hole( Please note these tuners Do Not fit 45 degree fixing tag); Offer you the option in many cases for a drop-in upgrade in both performance and appearance