Standard 75mm cold rolled shaped metal galvanised laths, readily available in either solid galvanised or which has a plastisol coating They consist of horizontal slats or bars that roll up and down close to a drum, allowing for for compact storage when Open and forming a strong barrier when Closed. https://tende-tagliafuoco41730.blog5star.com/39784770/the-2-minute-rule-for-industrial-shutters