TIMco 828SW Sela Washers are used when securing roofing sheets to create a watertight seal. When using spring head roofing nails, only a washer (SW) is required. If using hook bolts, you will also require a Sela Cover (SC) to cover the washer and nut to complete the seal. These washers are black and have a matte finish. The diameter is 28mm and the hole diameter is M8. They are made of plastic. The pack dimensions are 265 x 152 x 50 mm and the pack weight is 0.260 kg. The product code is 828SW and the size is M8 x 28mm. It is designed to fit screws with a diameter of 8.0mm. This is a Sela type washer. Please note: Due to geographical locations, we are unable to deliver to Highlands.