It is made of iron with black plating. Great replacement for your broken dirty or old control knob. Sure to make your guitar look new again! Knob Diameter: . 0.71 inch / 1.8cm Height: . 0.75 inch / 1.9cm Hollow Shaft Diameter: . 0.22 inch / 5.7mm Material: Iron Color: Black Package Contents: 8 x Guitar knob Only the above package content other are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.