I bought these to replace the tuners on my Fender FM-100 mandolin, which, although has a nice enough tone, is not the most expensive of instruments. The originals had plastic buttons glued to the tuner shafts which is not ideal, and after a series of frustrations, I decided to change them out for machine-heads with screw-fixed buttons and chose these based on cost. They do the trick and hold their tuning pretty well, however, there is quite a lot of play in the worm-wheel/gear arrangement with the result that it requires the strings to be tuned from flat all the time (which is good practice anyway); however, if I had a more expensive instrument I would probably go for either a Grover or Rubner unit. Having said that, despite the excessive play in the gearing, they work quite well for me and for the price are reasonable value