#1 square recess drive and trim head with a Type 17 tip for faster starts and to resist splitting in hardwoods. Coarse threads run approximately 2/3 up the shank to draw the decking tightly to the substrate. Pre-drilling is recommended near board-ends to reduce splitting. Use only with stable woods and wood substitutes for less noticeable fastening. Slender #7 shank is designed for finish work and trim. 316 stainless steel is recommended where superior corrosion resistance is needed.Simpson Strong Tie Co., Inc.