Countersunk bolts are flat headed bolt fasteners with hex socket drive into the head. Countersunk bolts have a cone type neck with flat head, flat head hex socket bolts, flat head socket cap bolts are other alias of hex head bolts. Countersunk bolts dimensions are defined in both metric and imperials sizes with unified national coarse pitch(UNC), fined pitch (UNF), fixed pitch(UN) and ISO metric thread profile. These are produced across all material categories and ASTM specifications but most commonly produced under F568 grade 8.8, 10.9,12.9, F593, BS, EN, ISO3506-1, SS304, SS316,2205, etc.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. Most hex socket countersunk head cap bolts are used in places where the surface of the part cannot be raised after installation. There are two types of parts to be fastened. The thickness of the head, after the screw is tightened, a part of the screw thread still does not enter the threaded hole. In this case, the countersunk head screw can certainly be tightened. The cone of the head of the countersunk head screw has a 90 ° cone angle. Usually, the apex angle of a newly purchased drill bit is 118 ° -120 °. Some untrained workers do not know this angle difference, and often use a 120 ° drill Reaming, which results in that the countersunk head screws are not strained when tightening the countersunk head screws, but a line at the bottom of the screw head, which is one of the reasons why the so-called hex socket countersunk head cap bolts cannot hold tight.1.The taper of the reaming hole should be 90 °. To guarantee it, it is better to be less than 90 °, 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 hex socket countersunk head cap bolt 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 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.

Product name	hex socket countersunk head cap bolt
Standard	DIN7991
Diameter	M3-M20
Length	≤800mm
Material	Carbon Steel, Alloy Steel, Stainless Steel, Brass
Grade	4.8,6.8,8.8,10.9,12.9 A2-70 A2-80 A4-70 A4-80
Thread	Metric
Finish	Plain,Black oxide, Zinc Plated(Clear/Blue/Yellow/Black), H.D.G, Nickel, Chrome,PTFE,Dacromet,Geomet,Magni,Zinc Nickel,Zinteck.
Packing	bulk in cartons (25kg Max.)+wood Pallet or according to customer special demand
Application	Structural Steel; Metal Buliding; Oil&Gas;Tower&Pole; Wind Energy; Mechanical Machine; Automobile Home Decorating