What Are Countersunk Bolts?

Countersunk head screws, also called flat head screws, are a type of construction part. The head is a 90-degree cone, similar to common wood screws. The head has a tool tightening groove, a zigzag, cross, hexagon, plum, pentagon, and so on.

Countersunk head screws

Countersunk head screws, also known as flat machine screws, have a 90-degree cone on the head, similar to common wood screws, a tool tightening groove on the head, and a flat, cross, and hexagonal shape.

On the surface of the mounting hole on the connecting piece, a 90-degree conical round socket is processed, and the head of the flat machine screw is in this round socket, which is flush with the surface of the connecting piece. Flat machine screws are also used in some occasions with round head flat machine screws. This kind of screw is more beautiful and is used in places where the surface can allow a little protrusion.

The screw plays the role of connecting two or more objects, and is an indispensable necessity in daily life or industrial manufacturing. With countersunk head bolts (with slot), countersunk head bolts (with tenon)

When buyers place orders for countersunk head screws, some are directly expressed in Chinese, and some more professional purchasers generally use country codes or specific letters to indicate them. The order of the countersunk head screws is represented by letters instead of KM, FM, KA and so on.

It is divided into countersunk head hexagon socket bolts, countersunk slotted bolts and so on according to various types of performance and functions.

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

Let's talk about the processing reasons: the head cone of the countersunk head screw has a 90 ° cone angle, and the apex angle of a newly purchased drill bit is usually 118 ° -120 °. Some workers who lack training do not know this angle difference. Often, a 120 ° drill is used to ream directly. This causes the countersunk head screws to be tightened rather than the conical surface of the head, but a line at the bottom of the screw head. This is one of the reasons why the so-called countersunk head screws cannot be tightened. It's not the screw's fault.

1. The reaming taper should be 90 °. To guarantee, it is better to be less than 90 °, but not more 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 change the smaller screw, or rather expand the hole smaller than expand the hole so that the diameter of the bottom hole becomes larger and the part is not tight. 3. If there are multiple countersunk screw holes on the part, be more precise during machining. Once the drill is crooked, it is difficult to see the assembly, but it can be tightened as long as the error is small, because when the screw is not very tight when tightening, Large (about no more than 8mm), when there is an error in the hole distance, the screw head will be deformed due to force when tightened, or it will be tightened.

specification	Screw head diameter	Screw head thickness	Screw rod diameter	Countersink hole diameter	Countersink depth	Through hole diameter
M2	3,8			4,5	3,0	2,5
M3	5,5			6,0	3,5	3,5
M4	7,0			7,5	4,5	4,5
M5	8,5			9,0	5,5	5,5
M6	10,0	6	5,8	11	6,5	6,5
M8	12,0	8	7,8	13	8,5	8,5
M10	15,0	10	9,8	16	10,5	10,5
M12	17,8	12,5	11,8	19	12,5	12,5
M14
M16	twenty four	16	15,9	26	16,5	17
M18
M20
M22
M24