From Calder
Copper nails fix lead into place only copper or stainless steel nails should be used. These ensure security, longevity and compliancy with relevant guidelines. Calder high-quality copper nails are specifically designed and manufactured to meet the requirements of British Standard BS-1202-1&2. The stipulated shank diameter for light duty use should be at least 2.65 mm and for heavy duty use at least 3.35 mm.