The Strong-Drive SDHR Combo-Head screw is a structural fastener designed for cross-laminated timber construction, mass timber construction and general interior applications. These partially-threaded, sturdy 0.394-in. and 0.472-in. diameter structural fasteners are designed to pull structural members together while providing excellent connection strength. The unique “combination” head allows for effortless driving using either a hex driver bit or T40 6-lobe driver bit. The SDHR Combo-Head has an interior-grade, blue-zinc coating, a robust knurled shaft and Type-17 point for fast starts and low-torque driving. Strong-Drive® SDHR COMBO-HEAD Screw — 0.315 in. x 4 in., Blue Zinc (100-Qty) (Pack of 39).