It would help if you asked a question or described symptoms instead of
being so vague that changing the tire might be the correct answer.
A 3-letter word for a harness piece might be a "bit".
Bit.
man
Rag?
There could be many answers, but I choose the word, "key". A Key signature is placed beside the clef signs in any piece of music.
Another 3 letter word for respect is awe.
3 letter word for old oldsmobile
A 3 letter word meaning pallid is wan.
A 3 letter word for AARP members is Boa.
pontoon
The 3 letter word for a group of kangaroos is mob.
the 3 letter word is BDY
another word for take to court is SUE.