The most common and most likely answer to this crossword clue is the 3 letter word PEG
I've seen this crossword clue in Financial Times
P
E
G
Buddy explains!
The straight part
We know that "Part of tuning system for violin" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case part of tuning system for violin = peg.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PEG mean?
PEG noun- A cylindrical wooden or metal object used to fasten or as a bearing between objects.
- Measurement between the pegs: after killing an animal hunters used the distance between a peg near the animal's nose and one near the end of its tail to measure its body length.
- A protrusion used to hang things on.
- A support; a reason; a pretext.
- A peg moved on a crib board to keep score.
- A fixed exchange rate, where a currency's value is matched to the value of another currency or measure such as gold
- A small quantity of a strong alcoholic beverage.
- A place formally allotted for fishing
- A leg or foot.
- One of the pins of a musical instrument, on which the strings are strained.
- A step; a degree.
- Short for clothes peg.
- A topic of interest, such as an ongoing event or an anniversary, around which various features can be developed.
- A stump.
- The penetration of one's (male) partner in the anus using a dildo.
- To fasten using a peg.
- To affix or pin.
- To fix a value or price.
- To narrow the cuff openings of a pair of pants so that the legs take on a peg shape.
- To throw.
- To indicate or ascribe an attribute to. (Assumed to originate from the use of pegs or pins as markers on a bulletin board or a list.)
- To move one's pegs to indicate points scored; to score with a peg.
- To reach or exceed the maximum value on (a scale or gauge).
- (typically in heterosexual contexts) To engage in anal sex by penetrating (one's male partner) with a dildo.
- To keep working hard at something; to peg away.