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. * material: plastic handle