For use with the BiForm Fixing Clips and Stop clips. Made from blackened 304 stainless steel, 40mm 6G with a No.1 square drive head. Also available in blackened 316 Stainless Steel. The head size has been designed to be easily unscrewed from between the boards with out causing damage. Use of a drill on low torque and leaving screws loose until the next board is in position is recommended.