Basically countersunk head up and down the straight line distance are about four millimeters in size. So to bury the countersunk head it is necessary to keep the countersunk head in the straight line of the dimensions of the countersunk head in more than four millimeters of the countersunk head size.
The use of countersunk head screws
1, countersunk head screws are mostly used in the need to install, the surface of the parts can not have a raised place, the fastening of the parts and there are two kinds of thick and thin, the so-called thick, that is to say, is fastened to the thickness of the parts is greater than the thickness of the countersunk head screws head, the screws are tightened, but also a part of the screw's threads did not enter the threaded hole. In this case, the countersunk head screws can certainly be tightened.
Often there is another situation, that is, the thickness of the parts to be fastened is less than the height of the head of the countersunk head screws, which is common in mechanical equipment in the sheet metal parts, such as hinges and chassis door and box connection; equipment, sheet metal cover and equipment connection and so on.
2, due to the small thickness of the parts, the sheet metal parts being fastened, the screw over the hole completely into a conical hole, in this case, when the countersunk head screws are tightened, the head of the screw is not a conical compression of the sheet metal parts, but the bottom of the root of the head of the screw with the top of the threaded hole squeezed to death, although it feels that the screws are tightened, but the sheet metal parts are jammed rather than pressed, in this case, although it feels that the screws are tightened, but the screw is tightened. In this case, although it is felt that the screw is tightened, the sheet metal part is really not tightened. This is a very common situation.
Countersunk head screws head vertebrae 90 ° cone angle, usually the top angle of the newly purchased drill 118 ° ~ 120 °, some lack of training workers do not know the angle difference, often directly with 120 ° of the drill reaming, which results in the countersunk head screws tightening is not the head of the conical surface of the force, but the bottom of the screw head of a line of force, which is also known as countersunk head screws can not be tightened! This is also known as countersunk head screws can not tighten one of the reasons.