Common tap specification range and standard code
As a key tool for machining internal threads, taps require a comprehensive range of specifications and standardized application codes to ensure the quality of threaded connections. Common tap specifications are primarily based on the nominal thread diameter, pitch, and thread profile. Different countries and regions have different standardization systems, resulting in a diverse range of tap specifications.
In the metric thread system, the specification range of taps covers multiple intervals from tiny diameters to larger diameters. The nominal diameter of small-size taps usually starts from M1, which is suitable for fine thread processing in precision instruments, electronic equipment and other fields, such as M1×0.25, M1.6×0.35, etc. These taps have a smaller pitch and require extremely high precision control during processing to avoid thread slippage or loose threads. Medium-size taps are the most widely used, with nominal diameters ranging from M3 to M24. The pitch varies depending on the coarse and fine threads. Coarse-thread taps have a larger pitch, such as M8×1.25, which are suitable for general mechanical connections; fine-thread taps have a smaller pitch, such as M8×1, and are often used in situations that require precise adjustment or axial force, such as the fixing bolts of machine tool guides. The nominal diameter of large-size taps exceeds M24 and can even reach M100 or above. They are mainly used for thread processing of large components such as heavy machinery and chemical equipment. Such taps are usually made of high-strength alloy materials to withstand the huge torque during the processing.
Imperial thread taps are specified in inches, based on the nominal thread diameter and the number of threads per inch. Common nominal diameters include 1/4 inch, 3/8 inch, 1/2 inch, and 3/4 inch, with threads per inch ranging from 20 to 8. The greater the number of threads, the finer the pitch. For example, 1/4-20 UNC represents a coarse unified thread tap with a nominal diameter of 1/4 inch and 20 threads per inch, suitable for general mechanical connections. 1/4-28 UNF, on the other hand, represents a fine unified thread tap, often used in applications requiring high thread precision, such as hydraulic system pipe connections. Imperial taps are widely used in Commonwealth countries and the United States, and are frequently used in the repair and assembly of imported equipment.
The standard designation for taps is an important identifier that distinguishes different standard systems and specifications. Different countries and organizations have developed corresponding standards. The International Organization for Standardization (ISO) has established ISO 529, a standard for taps. This standard provides unified regulations for tap dimensions, tolerances, materials, and performance, applicable to international trade and technical exchange. my country’s tap standards are designated GB/T. For example, GB/T 3464.1-2007 specifies technical requirements for hand taps, while GB/T 3464.2-2007 regulates machine taps. These standards align with international standards while also being appropriately adjusted to address my country’s actual production conditions to ensure tap quality and interchangeability.
In addition, there are standard codes from other countries, such as ANSI B94.9 in the United States and DIN 352 in Germany. ANSI B94.9 specifies in detail the dimensions and tolerances of taps for American unified threads. Its specification notation is similar to that of imperial threads, but differs in the precision grades. DIN 352 is the German tap standard, covering both metric and imperial thread taps and renowned for its high precision and stringent quality control. In practical applications, it is necessary to select a tap with the appropriate specifications and standard code based on the specific processing requirements and thread standards to ensure that the processed threads meet requirements for connection strength and sealing performance. Attention should also be paid to the tap’s precision grade, such as H1, H2, and H3. Different precision grades correspond to different thread tolerance zones, suitable for different fitting requirements.
