1.According to the connection force, there are common and hinged holes. The China Hex Bolts used for the hinged holes should be matched with the size of the holes for the transverse force.
2.According to the shape of the six head, round, square, countersunk head and so on, countersunk usually used in smooth surface without protruding place. Hex bolts is the most commonly used.
3.In order to meet the needs of locking after installation, there are holes in the head, these holes can make the bolts free from loosening when they are vibrated.
4.There is a special High Speed Fastening bolt on the steel structure. The head will be bigger and the size changes.
5.There also has anchor bolt, T bolt, square bolt and so on, and special studs for welding.