To determine the size of a Wittner Finetune peg you need measure the thickest part of the shaft of your current peg, which is below the collar, and select the Wittner Finetune Peg that is slightly thicker. Wittner Finetune pegs are measured by diameter right below the collar. They are available in different sizes.
You will need a reamer to fit these pegs. You should measure your pegs and order pegs slightly larger than the current size of your peg, and then ream them all out to the correct size during fitting.
