Lag screws, also known as lag bolts, are screws that are frequently used for building with wood. They have extra-strength holding power that makes them more durable than other types of screws. They have threads that lodge themselves into the wood so they don't have to rely on nuts to hold them in place. To screw lag screws into place, you can drill a slightly smaller pilot hole first and then drive the screw in so that its threading is embedded in the wood. Lag screws come in varying lengths and thicknesses, and they're normally made of metal. You can find silicon lag screws, too.

Lag screws are used in the construction of all types of projects, from railway trestles to home decks. To build decks using lag screws, first you have to plan out your deck. Figure out where you want it and what the dimensions will be. Measure out the length, width and height. After you have a detailed building plan, meet with a building inspector to have him look at your plans and advise you of any permits or inspections you'll need during the course of your project.

Once you're ready to begin building, mark out the height of the deck against the house. Drive batterboards into the ground a bit past the edges of the deck-to-be. Use mason's cord to set out the deck's perimeter, and check for evenness with a level. Dig footings for the deck that reach below the frost line and fill them with concrete; set the J-bolts into the concrete. The lag screws don't come in until you get to the point when you're ready to attach the ledger board to the house. First, drill pilot holes and then insert the lag screws through the boards and into the house.