Thread Content
Identification of Unified Inch Threads. Unified inch threads are widely used in the inch system; these threads are divided into three series: the coarse thread series UNC, the fine thread series UNF, and the ultra-fine thread series UNFF, in addition to a constant pitch series UN. Notation method: Thread diameter—TPI Series code—Precision grade Example: Coarse thread series 3/8—16 UNC—2A Fine thread series 3/8—24 UNF—2A Extra-fine thread series 3/8—32 UNFF—2A Constant-pitch series 3/8—20 UN—2A The first digit, 3/8, indicates the outer diameter of the thread in inches; to convert it to millimeters, multiply by 25.4, i.e., 3/8×25.4=9.525mm ； The second and third digits, 16, 24, 32, 20, represent the number of teeth per inch (the number of teeth over a length of 25.4 mm) ； The code letters after the third one, UNC, UNF, UNFF, and UN, are series codes, while the last two digits, 2A, indicate the precision grade. 2. Conversion of 55° cylindrical pipe threads: 55° cylindrical pipe threads originate from the imperial system, but they are widely used in both metric and imperial systems for connecting pipe fittings to pipes in order to transport liquids and gases as well as for installing wires. However, the codes used vary from country to country; it is necessary to convert these foreign codes into China’s own codes using the table below (conversion chart). The codes for 55° cylindrical pipe threads in various countries are listed in the table below. Country code: China – G; Japan – G, PF; United Kingdom – BSP, BSPP; France – G; Germany – R (internal thread), K (external thread); Former Soviet Union – G, TPУБ; ISO. Conversion for 55° tapered pipe threads: 55° tapered pipe threads refer to threads with a thread pitch angle of 55° and a taper ratio of 1:16. This series of threads is widely used around the world, and its designations vary from country to country, as shown in the table below. Convert the foreign codes in the table below to China’s codes. Country Code: China – ZG, R (external thread); United Kingdom – BSPT, R (external thread), Rc (internal thread); France – G (external thread), R (external thread); Germany – R (external thread); Japan – PT, R, ISO R (external thread), Rc (internal thread). Conversion of 60° tapered pipe threads: 60° tapered pipe threads refer to those with a thread pitch angle of 60° and a thread taper of 1:16; this type of thread is used in China’s machine tool industry as well as in the United States and the former Soviet Union. Its code was designated as K in our country in the past, then as Z, and is now changed to NPT. The thread code reference table is shown in the table below. Country Code: China – Z (old); NPT (new). United States – NPT. Soviet Union – B. Conversion of 5, 55° trapezoidal threads: Trapezoidal threads refer to metric trapezoidal threads with a thread angle of 30°. The thread standards in this series are relatively uniform both domestically and internationally, and their codes are also quite consistent; the thread codes are shown in the table below. Country Code: China – T (old), Tr (new); ISO – Tr. Germany – Tr; Former Soviet Union – Tr