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They are all hexagons. What is the difference between the outer hexagon and the inner hexagon?

 
Here, I will elaborate on their appearance, fastening tools, cost, advantages and disadvantages, and applicable occasions.

appearance

The outer hexagon bolt/screw should be familiar to you, that is, the bolt/screw with hexagon head side and no concave head;

 
The outer edge of the head of the hexagon socket bolt is round, and the middle is a concave hexagon. The more common is the cylindrical head hexagon, and there are pan head hexagon socket, countersunk head hexagon socket, flat head hexagon socket. Headless screws, stop screws, machine screws, etc. are called headless hexagon socket.

 
Fastening tool

The tightening tools for outer hexagon bolts/screws are common, which are wrenches with equilateral hexagon heads, such as adjustable wrenches, ring wrenches, open-end wrenches, etc;

The wrench shape for hexagon socket bolts/screws is “L” type. One side is long and the other side is short, and the other side is short. Holding the long side can save effort and tighten the screws better.

 
cost

The cost of outer hexagon bolt/screw is low, almost half of that of inner hexagon bolt/screw.

advantage

Outer hexagon bolt/screw:

Good self-marketing;

Large pre-tightening contact area and large pre-tightening force;

The length range of full thread is wider;

There can be reamed holes, which can fix the position of parts and bear the shear caused by transverse force;

The head is thinner than the hexagon socket, and in some places the hexagon socket cannot be replaced.

 
Hexagon socket head bolt/screw:

Easy to fasten;

Not easy to disassemble;

Non-slip angle;

Small space;

Large load;

It can be countersunk and sunk into the interior of the workpiece, which is more exquisite and beautiful, and will not interfere with other parts.

 
shortcoming

Outer hexagon bolt/screw:

It occupies a large space and is not suitable for more delicate occasions;

It cannot be used for countersunk head.

 
Hexagon socket head bolt/screw:

Small contact area and small preload;

There is no full thread beyond a certain length;

The fastening tool is not easy to match, easy to screw and replace;

Use a professional wrench when disassembling. It is not easy to disassemble at ordinary times.

 
Applicable occasions

Hexagon bolts/screws are applicable to:

Connection of large equipment;

It is applicable to thin-walled parts or occasions subject to impact, vibration or alternating load;

Places with long thread requirements;

Mechanical connection with low cost, low power strength and low accuracy requirements;

Places without considering space.

Hexagon socket head bolts/screws are applicable to:

Connection of small equipment;

Mechanical connection with high requirements for beauty and accuracy;

Situations requiring countersink;

Narrow assembly occasions.

 
Although there are so many differences between the outer hexagon bolt/screw and the inner hexagon bolt/screw, in order to meet more use requirements, we do not only use one kind of bolt/screw, but also need to use multiple fasteners and screws together.