In automotive assembly process, a lot of different screws are used. They are usually used for locking and rotating functions. It is very important to make sure about the correct dimension and In automotive assembly process, a lot of different screws are used. They are usually used for locking and rotating functions. It is very important to make sure about the correct dimension and grade of bolts and nuts to assemble the car for the specific application. There are car assembly parts made by auto bolt, which include turning, forging, rolling, heat treatment, plating, etc. Its types include screws, nuts, bushings and other car connections. These machined metal fasteners are also applied in other related industries, not only automotive assembly. It should be noted that the most common type of automotive screw used in the automotive industry are the head bolt, nut and the hex cap screw, which is a combination between a bolt and a nut. If any of the fasteners come loose, you will have a problem with your vehicle. For instance, a defect of screw in the engine or powertrain system can prevent your car from starting, while unstable fasteners in the suspension or brakes can lead to tragic car accidents.grade of bolts and nuts to assemble the car for the specific application.