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