How Are Hex Bolts Classified?

Update:Dec 30, 2022

How are hex bolts classified?

Hex bolts are hex head bolts (partially threaded) - class C and hex head bolts (full thread) - class C. Also known as hexagon head bolts (coarse) hair hexagon head bolts, black iron screws.

Hex bolt: A type of fastener consisting of a head and a screw (a cylinder with external threads), which needs to be matched with a nut to fasten two parts with through holes.

This form of connection is called a bolt connection. If the nut is unscrewed from the bolt, the two parts can be separated, so the bolted connection is a detachable connection.


1. According to the force-bearing mode of the connection, there are ordinary and reamed. Bolts for reaming should match the hole size and be used when subjected to lateral forces.

2. According to the shape of the head, there are the hexagonal head, round head, square head, countersunk head, etc. Generally, the countersunk head is used where the surface is smooth and has no protrusion after connection because the countersunk head can be screwed into the parts. The head can also be screwed into the part. The tightening force of the square head can be larger, but the size is large. Hex heads are the most commonly used.

In addition, in order to meet the needs of locking after installation, there are holes in the head and holes in the rod. These holes prevent the bolts from loosening during vibration.

Some bolts without threads need to be thinned, called thin-waist bolts. This type of bolt facilitates variable force connections.

There are special high-strength bolts on the steel structure. The head will be larger. Dimensions also change.

In addition, there are special purposes: T-slot bolts, which are mostly used on machine tool fixtures, have special shapes, and both sides of the head must be cut off. Anchor bolts are used to connect and fix machines and the ground, and come in many shapes, such as the U-shaped bolts mentioned above.

There are also special studs for welding, one end is threaded and the other end is not, which can be welded on the part, and the other end is directly screwed with the nut.

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