Buytra L-shape Square Shape Tip Tuning Hammer Tuner Spanner Tool The shaft is made out of steel. Used for tuning of Guzheng and for most machine devices that have quadrilateral opening Side Length Of The Quadrilateral: Approx 6.5mm.. Overall Length:. Approx 16cm / 6.3 inch. Handle Length: Approx 10.5cm / 4.1 inch..