Lag bolts are heavy-duty fasteners designed for securing large wooden structures or heavy materials. They have a thick, coarse thread that provides a strong grip in wood, making them ideal for applications like building decks or framing. Typically made of steel, lag bolts require a pre-drilled hole for installation. They are driven in using a wrench or socket, allowing for a tight fit. Their durability and strength make them a popular choice in construction and woodworking projects.