SPAX #10 x 3-1/2in. Flat Head Stainless Steel Screw with Double Lock Thread - 1 LB Box The Double ThreadLok design pulls and holds boards tight, preventing screws from backing out and boards from squeaking as lumber dries out. Our Trim head design offers pleasing aesthetics across the deck surface. The deep square drive offers excellent bit engagement. Better bit engagement means quicker installation with less effort. Check out our Threads!! Our patented thread technology allows the screw to be driven faster, is easier to install, and reduces splitting in wood. Let SPAX take some of the hassle out of your next project.