Pegs for [[double bass]] and [[guitar]] family instruments are usually geared, and are called tuning machines or [[machine head]]s. They often use a [[worm gear]]. The [[gearing ratio]] varies; while higher ratios are more sensitive, they are also more difficult to manufacture precisely. Machine heads may be open, with exposed gears, or closed, with a casing around all the gears.
Geared pegs for [[violin family]] instruments also exist, although they have not gained wide use, which has to do with the extensive and irreversible physical modification that must be made to the peg box in order to mount them, which is often viewed as ruining the aesthetics of the instrument, combined with a bad reputation they acquired due to poorly designed early models that were prone to failure (e.g. Stripped Gears), often with catastrophically damaging results, though they've made improvements to them & are being used on Electric Bowed instruments (e.g. Viper Violin, Cobra Cello from WoodViolins)
The most recently marketed geared pegs of this sort use [[planetary gears]] designed to fit inside a case shaped like a friction peg. They have seen some adoption as they look identicalalmost toexactly like friction pegs (but w/ the Gears inside), require no more modification of the instrument than justa changingnew outset theof tunersfriction pegs, and eliminatingmake fine tuners from the tailpiece which like on a Baroque Stringed instrument livens up the sound by allowing the top to vibrate more freelyunnecessary. They are also durable and less sensitive to changes in temperature and humidity.<ref>{{cite web |title=Information – Perfection pegs |url=https://perfectionpegs.twofold.com.au/information/ |website=perfectionpegs.twofold.com.au |access-date=10 August 2019}}</ref> They are popular on banjos.<ref>{{cite web |title=Banjo Tuning Pegs Planetary vs Geared |url=https://www.folkmusician.com/blogs/blog/banjo-tuning-pegs-planetary-vs-geared |website=Folkmusician |language=en |date=30 March 2018}}</ref> All that said a luthier named Bodo Vosshenrich uses Geared tuners when he builds Bowed instruments for practicality reasons.
