Pegs.

String instrument pegs are an essential component of many stringed instruments, such as violins, violas and cellos. They are used to adjust the tension of the strings, which in turn affects the pitch of the instrument.

The primary function of pegs is to tighten or loosen the strings to bring them to the correct pitch. By turning the pegs, a player adjusts the tension of each string, raising or lowering the pitch as needed.

Most traditional string instruments, such as violins and cellos use wooden pegs, often made from hardwood like boxwood, rosewood, or ebony.

Sometimes, small amounts of peg compound (a wax-like substance) are used to reduce friction and prevent the pegs from sticking or slipping. However, this must be used carefully to avoid overuse or damage to the instrument.

In Tamsta music store you can find a great choice of string instruments pegs.

https://tamsta.com/lt/466-derinimo-mechanika

https://www.petzkolophonium.com/shop/lng/en/accessories/pegs/?xoid=343aab60faf540a0132eb8daab08475b