These gray silicone washers are twice as thick as our black EPDM washers. The extra resiliency allows them to seal the nail hole even if not driven at right angles to the sheet. Do not overdrive! Washer should just begin to "balloon" under the nail head, but not bulge over nail head. Most Metal Roofing manufacturers recommend minimum nail penetration of at least 1" into purlin. Nails are double-dipped in molten zinc.
