Countersunk hole is to drill holes on the board with a flat head drill needle or a causeway knife but cannot drill through (that is, half through holes). The transition part of the hole wall at the outer/maximum aperture and the hole wall at the most small hole is parallel to the pcb surface, and the part connecting the large hole is a plane, not a bevel.
Through hole, as the name suggests, that is, transparent, through, can pass through the appropriate size of the object or liquid hole, the role is:
a. for connection, can be made into threaded through holes.
b. make the cylinder of the piston engine.
c. under the pump, etc., used to transport liquid, gas, dust loading objects, etc.
d. in life, the clothes and pants we wear are also examples of through-hole applications.
The general crimping hole is a copper-plated plug-in hole. Because of the special design of the element foot, the structural tension of the inserted hole can be firmly connected with the hole. The advantage is to reduce a wave crest welding set for welding such components; If the hole is not welded in the end, then replacing the part will be an easier task. Of course, multiple changes will affect the reliability of the hole. The element pin required to crimp the hole is generally with an expansion function, rather than a threaded function. Some will be welded again later when the other components have been welded, and some will only be welded.
Before the implementation of the GB-1984 standard, the countersunk hole was divided into three names:
1. the head of the fastener is completely sunk into the step hole of the part, called the countersunk hole
2. the head of the fastener is not completely sunk into the step hole of the part, called the countersink hole
3. the head of the fastener is basically not sunk into the parts, and only the holes on the surface of the parts are called fisheye pits
The difference between countersunk hole and countersunk hole is that the upper part of the bolt hole is reamed: countersunk hole is a straight barrel structure; The countersunk hole is of 45 degree construction, which is smoother than the countersunk hole. The upper reaming of the bolt hole can accommodate the bolt head so that the screw head is not higher than the surrounding surface. Countersunk hole and countersunk hole are just two different names.
Generally, the countersunk head is used in places where the surface is smooth without protrusions after connection, because the countersunk head can be screwed into the part. Round heads can also be screwed into parts. The tightening force of the square head can be larger, but the size is large. In addition, in order to meet the needs of locking after installation, there are holes in the head and holes in the rod part, which can make the bolt not loose when it is subjected to vibration. Some bolts do not screw the rod to be thin, called thin waist bolts. This kind of bolt is good for connection under variable force. There are special high-strength bolts on the steel structure, the head will be larger, and the size will also change.
In addition, there are special uses: T-slot bolts, the most used on the machine tool fixture, the shape is special, and the two sides of the head should be cut off. Anchor bolts, used to connect the machine to the ground, are available in many shapes. U-shaped bolt, as described above. Let's wait. There are special studs for welding, one end has a thread and one end does not, which can be welded on the part, and the other side directly screws the nut.
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