It is used to protect metal roof elements or devices against the effects of discharges. Free-standing mast. Under the concrete base, it is recommended to use the 94308222 washer for roofs covered with roofing felt or 94308221 for roofs covered with a membrane. The cross clamp for connecting the wire is sold as a set. The mast is made of aluminum or copper, and the stabilizer is made of stainless steel.