Sela Washers used are used when securing garage roofing sheets to create a watertight seal.
When using spring head roofing nails just a washer is required as the head of the nail will cover the entire washer to provide a watertight seal.
If using hook bolts you will also require a sela cap to cover the washer and nut to complete the seal.
Available in M6 x 28 outside diameter and M8 x 28mm outside diameter.