Just as with SKK's pots and pans, their glass covers also adhere to the highest standards. Nevertheless, glass is a fragile material that can be damaged by shock or excessive force. This can include: overtightening the screw which holds the knob in place (by using excessive force with tools or pliers). The lid can become energized and break. To properly tighten the knob, hold the screw (on the inside of the glass cover) in place with your thumb and tighten the knob with your other hand. No excessive force is necessary...at all. Also, please make sure the screw's washer remains installed; otherwise the knob will not be properly secured, and the glass could break.