Since wood decks have many thin planks and must withstand harsh environmental conditions, deck screws are designed to accommodate the challenges of this application. They must resist corrosion, drive easily, and lay smoothly against the deck surface, called countersinking. For these reasons, many deck screws are self-countersinking, self-drilling, and coated with materials that won't rust.
Like other screws, deck screws come in a wide variety of lengths and widths, called shanks. They also use different shapes of driver, the part on the screw head that allows a screwdriver to dig in to the wood and rotate. A popular head shape is a square, because it holds the driver and doesn't strip as easily as Phillips heads.
One feature of deck screws that makes them easy to install is the sharpness of their point. They often come to a very sharp, narrow point, to reduce the necessity of drilling pilot holes. Especially in a soft deck wood like cedar, these screws can be fastened without needing to pre-drill the hole, called self-tapping.
Secondly, screws designed for a deck will propel themselves into place because of their unique shank design. The thread of the screw is measured in degrees, so a shallower degree means more thread along the length. These threads spread out the force, so the screw takes less effort to put in, yet it is still difficult to pull out. Some types of deck screws are lubricated so they slide into the wood even more easily.
The most important characteristic of deck screws is their resistance to corrosion. This is determined by the type of metal or metal coating that doesn't succumb to rust. For example, zinc plated (galvanized), stainless steel, high copper content, and ceramic-coated screws are appropriate for exterior use on decks or fences because they won't stain the timber.
Recently, composite decks made out of specially developed materials or pressure-treated wood have become popular. Since these deck planks are not standard lumber, special deck screws had to be designed to work with this material. Regular, self-countersinking screws caused the plank to "mushroom," meaning that the material pulls up in a hump around the screw head. Make sure to use the screws that the composite deck manufacturers recommend to avoid such issues.