Stålviks A4 Class C5 Marine Acid-Resistant Deck Screw for hidden installation. 4.8 x 60 is used for decking boards with a thickness of 22–35 mm. (e.g., 22, 28, 32, 34 mm) Stålviks screws feature a unique angle that provides maximum clamping force in both the top and bottom boards. The weak point in the joint is always the decking board itself, where the screw has the least material to grip; therefore, choosing a screw longer than 60 mm is a complete waste of money. With our angle and our extremely stable tool, the screw has more than twice as much grip in the joist as in the decking board. We recommend not countersinking the screw any further than the exact fit achieved with Stålvik’s tool and Stålvik’s bits. The more you countersink the screw, the weaker the joint’s strength becomes. Special screw designed for use with the installation tool. Equipped with a nail-drill tip and a reverse thread under the head that presses the decking board against the underlying joist. There are simpler solutions with two different thread pitches, but they can’t compare to a reverse thread, which pulls the wood together much more effectively—which is especially important when working with hidden screws, since the screw doesn’t have as much material to grip into as when you screw from above. This is a slightly more expensive solution, but the results are much better. Camo and other premium manufacturers use the same technical solution. Material: Acid-resistant A4 stainless steel. The screw is compatible with several different tools on the market, such as Essve, Camo, Fast, Heco, Gunnebo, MFT, and others. (NOTE: The bits vary by brand, so it’s important to use the correct bit even if the screw fits different tools) The Stålviks tool is adjustable from 90 mm to 150 mm NOTE! We recommend only A4 acid-resistant (not C4 or A2 stainless steel) The screw is manufactured for professionals and discerning DIYers and offers the very best installation properties. A4 offers the best corrosion protection available on the market.