The cooker knobs are metal , high temperature resistant, high friction resistant, sturdy and to use. Unique appearance , with smooth , very easy and comfortable to grip. It is very easy and comfortable to grip, and it's also very easy to install. 8mm Inner hole is for easily mounting, it's really great for you to replace the damaged for your Stove Cooker. The mark on the knob could help you recognize the correct direction to adjust.