The American standard thread is also known as the unified thread. It mainly has the following series:
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UNC (Unified National Coarse): Suitable for occasions requiring high tensile strength, such as general mechanical connections and structural component connections.
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UNF (Unified National Fine): Commonly used in parts where high precision is required, fine adjustment is needed, or frequent disassembly and assembly are involved, such as in instruments, meters, and precision machinery.
The marking method of American standard threads includes the following parts: thread diameter, number of threads per inch, series code, and precision grade. Example: For the coarse thread series 3/8—16 UNC—2A, 3/8 represents the outer diameter of the thread, which is converted to the metric unit as 9.525mm; 16 is the number of threads per inch; UNC is the series code, indicating the unified coarse thread; 2A is the precision grade.
The series codes of American standard threads and their meanings are as follows:
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UNC: Unified National Coarse thread
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UNF: Unified National Fine thread
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UNEF: Unified National Extra Fine thread
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UN: Constant pitch series
The precision grade 2A indicates that the thread tolerance is the standard medium precision. Other precision grades such as 6A, 7A, 8A, etc., respectively represent higher precision and tighter tolerance limits.
The dimensional specifications of American standard threads and the corresponding drill diameters. For example, NO.2-56 UNC indicates a coarse thread with a diameter of 2 inches, and its drill diameter is 1.94 inches. Similarly, for other specifications such as NO.3-48 UNF, NO.4-40 UNC, etc., there are corresponding drill diameter sizes.
The marking method of American standard pipe threads includes the thread diameter and the series code, such as 1/2-13 NPT or 1/2-13 NPS, where NPT is the abbreviation of "national pipe thread" and NPS is the abbreviation of "nominal pipe size".
The specifications of American standard electrical threads and the drill diameters. For example, 2BA, 3BA, 4BA, 5BA, 6BA, etc., all have corresponding drill diameter sizes.
Common ones include pan head, round head, flat head, hexagon head, socket head, and raised countersunk head, etc. Pan head and round head screws have a relatively round appearance and provide a large bearing area at the head. Flat head and raised countersunk head screws can make the surface flatter and are suitable for occasions where a smooth surface is required. Hexagon head and socket head screws are convenient for tightening and loosening with tools such as wrenches.
There are slotted, Phillips, socket, and Torx slots, etc. Slotted and Phillips slots are more common and are suitable for general assembly and disassembly. The Torx slot has better torque transmission performance and anti-slip performance. The socket slot is suitable for occasions that require greater torque and higher precision.
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Electronic Devices: For example, in the fixation of circuit boards and the assembly of casings inside mobile phones, computers, tablets, etc., generally smaller-sized American standard screws are used, which require high precision and an aesthetically pleasing appearance.
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Mechanical Manufacturing: Widely applied in the connection of small mechanical parts and the assembly of instruments and meters, such as small motors, speed reducers, and measuring instruments.
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Automobile Manufacturing: Used for the fixation of automotive interior parts and the connection of components in the electronic control system, such as instrument panels, door interior panels, and sensors.
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Aerospace: American standard small screws are also used in the assembly of some small aerospace components and aerospace electronic devices, with extremely high requirements for the precision, strength, and reliability of the screws.
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Furniture Manufacturing: Especially for American-style furniture, American standard screws may be used for frame connection and hardware installation.
