Yes just to clarify-  those screws are not supposed to function to 'hold' the string's tuning in place after every time you tune. They are just supposed to make it a little easier or harder to turn the tuning peg- tightening or loosening the tension of the tuning machine, not the string. As Dusty said, it might be only needed once in a great while. If you notice a tuned string slipping lower in pitch because the peg will not hold it at its note, then that might be a good time to tighten the screw of that peg just a little- only until the peg holds the string in tune sufficiently. If you tighten the screws too much they can strip/stop working.

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The tuners in the photo @lilley-pad posted are of very nice planetary-type tuners and are not inexpensive.  In the photo, they're on what I'm pretty certain is a Blue Lion dulcimer.  The type of tuners pictured can be seen here on a Blue Lion: https://www.bluelioninstruments.com/Dulc.pix/IIW.jpg  

updated by @robin-thompson: 05/05/25 06:29:12PM

You should not normally have to do anything with those screws. Over time, however, the tuning pegs might get too stiff or loose and you adjust them with those screws.  You probably only need to adjust them once every ten years or so.  If you don't have a problem tuning your strings, don't mess with those screws.

Some tuning pegs have much tinier little screws, and sometimes they are on the other end of the post.

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Dusty T., Northern California
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That is the same impression I got, matt. On very simple instruments you often see these types of screws that are meant to hold the tension of the string, and typically they cannot support more than 10 lb at most

Anything beyond that starts to dig into the plastic

updated by @nate: 05/05/25 03:51:32PM

Those appear to be ukulele tuners.  I tried them once, I thought they worked poorly and never used them again as they do not work well with steel strings.   as far as I could tell, you tighten the screws and then tune the string and hope the tuner holds.

Hi kids just trying to increase my education here I noticed a pair of tuning pegs. I was wondering what they are called and what are the little adjustment screws on the end for?Are you supposed to loosen the screw and then tune the string and then tighten the screw back down tight, I don't get it.  Seems like an awful lot of work if that's the case. Hope the photo was attached