Lag Bolts are used for heavier materials because they can withstand a lot of weight. They are of the strongest and toughest screws in the market and are commonly known as Lag Screws. Their general use is to connect heavy lumbers and materials. Lags are not used with a nut or fasteners, they work by burrowing the coarse threads to create a type of joint friction. In simpler words, lag bolts are screws with a wrench head and wood screw threads that are terminating at one point.