... POM, 4.5mm stainless steel, these components are matched with clutches, so our engineers will guide you which spec to use.Roller ... thickness, different sizes such as 28mm, 38mm, 36mm to match with clutches.Top rail: Optional accessory, made from aluminum alloy, choosing ... Cover: Optional accessory, made from aluminum alloy, looks more artistic with cover.Bottom rail and end cap: Made from aluminum alloy ...