Simpson 0.470 x 6 1/4" Strong-Drive SDHR COMBO-HEAD Screw Blue ZincModel No. SDHR31614 R25 Finish. Blue Zinc Coated Length. 6 1 4 Head Diameter (in.) 0. 669 Shank Diameter (in.) 0. 315 Drive Type. T40 6 Lobe or Hex Head Head Type. Combination Thread Length (in.) 4 3 8 Point Type. Type 17 Point 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 structural fasteners