How to choose taps?
Thread is the most common method to connect mechanical parts, and tap is the most commonly used tool to process internal thread. Proper selection of taps for internal thread processing can ensure the quality of thread connection and improve the service life of taps.
Select tap tolerance zone
All domestic machine taps are marked with pitch diameter tolerance zone Codes: H1, H2 and H3 respectively indicate the same position of tolerance zone, but the tolerance values are different.
The tolerance zone code of hand tap is H4, the tolerance value, pitch and angle error are larger than machine tap, and the material, heat treatment and production process are not as good as machine tap. H4 may not be marked according to regulations.
The grade of tolerance zone of internal thread that can be processed by pitch diameter tolerance zone of tap is as follows: the code of tolerance zone of tap is applicable to the grade of tolerance zone of internal thread
Some enterprises use imported taps. German manufacturers often mark them as iso14h, iso26h and iso36g (international standard iso1-3 is equivalent to national standard h1-3). In this way, the code of tolerance zone of taps and the tolerance zone of Machinable internal threads are marked.
How to choose the standard of tap thread?
There are three common systems of common thread: metric system, English system and unified system (also known as American system). Metric system is a thread with 60-degree tooth angle in mm. For example: m8x1-6h represents the tolerance zone of 8 mm diameter metric fine thread, 1 mm pitch and 6h internal thread.
Inch system is a thread with 55-degree tooth angle in inches. For example: BSW 1 / 4-20 means 1 / 4-inch diameter, coarse pitch 20 teeth per inch, this thread is rarely used. Another unified system is in inches, tooth angle of 60 degrees of thread.
The diameter is less than 1 / 4 inch, which is usually indicated by numbers. From No. 0 to No. 12, the diameter specifications are 0.06 inch to 1 / 4 inch respectively. The United States still mainly uses unified thread.