The cylinder head bolt plays an important role in the proper operation of the internal combustion engine. Its function is to hold the cylinder head on the engine block by inserting a seal. It is important that the cylinder head bolts are properly installed. The tightening sequence and torques must also be observed. If the cylinder head needs to be removed for repair, it must be reassembled with strictly new cylinder head bolts after service because these bolts must be tightened to the torque that will result in the final elongation of the bolt, thus exerting maximum tightening force. The cylinder head bolt is made of special steel and has a coating on its surface that reduces the frictional force, thus helping to minimize deformation when tightened to torque and then angle.