3/8" X 6" - 304 Grade Stainless Steel lag Screws, Hex Head Fasteners, - AntiqueHardwareDepot.com
3/8" x 4" Simpson Strong-Tie Titen HD Countersunk Head Heavy-Duty Screw Anchor Zinc Plated, 50/Box
KINJOEK 50 Packs 1/4-20 x 3/4 Inch Flat Head Socket Cap Screws, Allen Socket Drive, 304 Stainless Steel 18-8, Full Thread, Bright Finish, Heavy Duty Hexagon Countersunk Machine Screw Drive: Amazon.com: Industrial & Scientific
Tek Screws for Thick Steel - Heavy Duty Self Drilling Metal Screws