Bearings facilitate to mount the deck on an axle. Nearly all bearings are graded according to a scale called an ABEC scale. Standard size of bearings is Industrial 608 and bearings are by and large made of steel. Other hardware includes a set of bolts, generally 8 in a set (10-32 bolts). An Allen (or crosshead) is also part of hardware. Also, used are self-lock nylock nuts. Skateboards contain two metal trucks, which are generally made from aluminum alloy. These join the wheels to the deck. The trucks are made up of a base plate and a hanger. The base plate is screwed to the deck and the hanger holds the axle. There are also rubber grommets or bushings linking the hanger and the base plate, which help the board movement and turn.