Proline 3+3 Tuning Machine Set, Open Gear Plank Chrome/Pearloid 3+3 Tuning Machine Set, Open Gear Plank Chrome/Pearloid The ProLine 3+3 Tuning Machine Set, Open Gear Plank are standard size and designed to work with most classical guitars The tuning pegs are 3/8' in diameter The ProLine 3+3 Tuning Machine Set, Open Gear Plank are standard size and designed to work with most classical guitars The tuning pegs are 3/8' in diameter