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countersunk socket bolt:definition,usage,types,Instructions,Precautions


Countersunk socket bolt

Countersunk head screws, also called countersunk screws, are also called flat machine screws, which are a kind of construction parts. The head is a 90-degree cone, which is similar to a common wood screw. The head has a tool-tightening groove, such as a font, cross, hexagon, quincunx, pentagon, etc.

Screws are used to connect two objects. Generally, the head of the screw protrudes above the surface of the object to be connected, causing the surface to lose its flatness. Countersunk screws can sink under the surface to make the surface flat. For harder objects, countersink holes need to be drilled in the corresponding position of the countersunk head. In short, the countersunk head means that the head of the screw can keep the surface flat after installation.



A countersunk screw, also known as a flat machine screw, has a 90-degree cone on its head, similar to common wood screws. The head has a tool-tightening groove, such as a font, cross, hexagon, etc.


On the surface of the mounting hole on the connecting piece, a 90-degree conical round socket is machined, and the head of the flat machine screw is in the round socket and is flush with the surface of the connecting piece. Flat machine screws are also used in some occasions with half-round head flat machine screws. This kind of screw is more beautiful and is used in places where the surface can be slightly protruding.

Screws play the role of connecting two or more objects and are an indispensable necessity in daily life or industrial manufacturing. There are countersunk head bolts (slotted), countersunk head bolts (with tenon)


According to various types of performance and function, it is divided into countersunk hexagon socket bolts, countersunk slotted bolts, etc.


Countersunk head screws are mostly used after installation, the surface of the parts can not be raised, and the fastened parts have two thicknesses, the so-called thick, which means that the thickness of the fastened part is greater than that of the head of the countersunk screw Thickness. After the screw is tightened, there is still a part of the screw thread that does not enter the threaded hole. In this case, the countersunk screw can definitely be tightened. There is usually another situation, that is, the thickness of the fastened parts is less than the height of the head of the countersunk screw, which is common in sheet metal parts in mechanical equipment, such as the connection of the hinge of the chassis and the door and the box; the sheet metal of the equipment Connection of cover and equipment, etc. Due to the small thickness of the part, the screw through hole of the fastened sheet metal part is completely a conical hole. In this case, when the countersunk screw is tightened, the screw head is not a conical surface to compress the sheet metal part , But the bottom of the screw head and the top of the threaded hole are squeezed. Although the screw feels that the screw is tightened, the sheet metal is stuck instead of being pressed. In this case, although the screw feels that the screw is tightened, the sheet metal The gold piece is indeed not tightened. This is a very common situation.

Let me talk about the reason for processing: the head cone of the countersunk screw has a 90° taper angle. Usually the top angle of the newly purchased drill bit is 118°-120°. Some workers who lack training do not know this angle difference. It is often used directly to ream the hole with a 120° drill bit, which results in that when the countersunk head screw is tightened, it is not the conical surface of the head that is difficult, but the line at the bottom of the screw head is difficult. This is one of the reasons why the so-called countersunk screw cannot be tightened. , This is not the fault of the screw.


1. The taper of the reaming hole should be 90°, and it should be guaranteed that it should be less than 90° rather than greater than 90°. This is a key trick. 2. If the thickness of the sheet metal is less than the thickness of the head of the countersunk head screw, you can replace the screw with one size smaller, or it is better to ream the hole smaller than ream so that the diameter of the bottom hole becomes larger and the parts are not tight. 3. If there are multiple countersunk screw holes on the part, be more precise when processing. Once drilled, the assembly will be difficult to see, but as long as the error is not large, it can be tightened, because when tightening, if the diameter of the screw is not very Large (approximately no more than 8mm), when the hole pitch has an error, the screw head will be deformed due to the force when it is tightened or it will be tightened.

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