This section provides an overview for inch screws as well as their applications and principles. Also, please take a look at the list of 9 inch screw manufacturers and their company rankings.
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An inch screw is a screw whose basic dimensions are standardized in inches.
Screws widely used in Japan are metric screws, and their basic dimensions are standardized in meters. An inch screw is widely used in the United States, the United Kingdom, and Canada.
Inch screws are mainly used in the following applications:
Other applications include aircraft and imported furniture.
The principle of an inch screw is the same as that of a regular screw. By lifting a heavy object using the screw's slope, the screw body is pulled to generate a large fastening force, or axial force. The reason why the screw does not loosen when tightened is because of the frictional force on the screw's slope. The frictional force is greater than the force of the slope component of gravity, and the fastening force is maintained without sagging.
Inch screws can be broadly classified into two types: unified screws and wit screws.
Unified threads are a standard defined by ANSI (American National Standards Institute) in the United States. There are two types of unified threads: unified coarse threads and unified fine threads. The fine thread screws have a smaller thread pitch than the coarse thread screws. The finer pitch is less likely to loosen, but it requires more turning when fastening, which reduces workability. The same is true for metric screws, which are available in two types: coarse and fine.
The wit screw is the world's first standardized inch screws. The wit screw is known as the world's first standardized screw. While metric and unified screws have a thread angle of 60°, the Witt screw has a thread angle of 55°.
Handling precautions for inch screws are the same as for metric screws. However, care must be taken to avoid misuse, such as using a metric screw in the threaded hole of inch screws. It is difficult to distinguish between a metric screw and inch screws by looking at the screw itself.
It is necessary to measure the outside diameter and pitch of the screw using calipers. If you feel something is wrong when tightening a screw into a screw hole whose specification is not known, we recommend that you measure the size of the screw instead of forcing yourself to do so.
Coarse-grained screws are abbreviated UNC, and fine-grained screws are abbreviated UNF. Inch screws are written using these fractions and standards in the following order: (1) screw nominal (thickness), (2) number of threads, (3) standard, and (4) length. An example is as follows.
Another wit screw is indicated by adding "W".
*Including some distributors, etc.
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