The general countersunk head is used where the surface is smooth and not raised after the connection is required, because the countersunk head can be screwed into the part. The round head can also be screwed into the part. The tightening force of the square head can be larger, but the size is very large.
In addition, in order to meet the needs of the lock after installation, there is a hole in the head, the rod has holes, these holes can be caused by the vibration of the bolt not to loose.
Some bolts without thread of light rod to do thin, called waist bolts. This kind of bolt is beneficial to the connection of the variable force.
The steel structure has special high-strength bolts, the head will be bigger, the size also changes.
In addition there are special uses: T-groove bolts, machine tool fixture on the most, the shape of special, the head on both sides to cut off. Anchor bolts, used for machine and ground connection fixed, have many kinds of shapes. U-shaped bolts, as described above. Wait a minute.
There is also a special stud for welding, a thread end is not, can be welded on the part, the other side directly screw the nut.