Some questions about threads
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I looked up some information online, and threading is really a mess; I’ve seen that not many people, either online or among my colleagues, really understand it properly. I was also confused. I roughly understand the basics of pipe threads, but I have a few questions: 1. What type of thread does “18G” on the thread gauge refer to? 55 degree unsealed G thread, 18 teeth per inch? Then why isn’t the pitch specified? 2. I’m curious about the thread specifications for those threaded plugs we often talk about – whether they are 6-inch ones or 1-inch ones
1. The “18G” on the gauge refers to a thread with 18 threads per inch; it indicates the number of threads, the pitch, and the type of pipe thread. "G” indicates that the thread follows metric standards, while the 55-degree non-sealing G thread is defined in inches. Its pitch generally does not need to be specified, because for standard pipe threads, the pitch and diameter are in a fixed ratio; thus, the pitch can be calculated based on the thread diameter. 2, 6-inch thread plugs and 1-inch thread plugs refer to the nominal diameter of the pipe, not the thread specification. A value of 6 indicates a pipe diameter of approximately 20 mm, with the corresponding thread specification usually being G3/4 ； 1 inch indicates a pipe diameter of approximately 25 mm, with the corresponding thread specification usually being G1. .
Just as you said, the threads are very complex and messy. At present, there are many types of threads we can work with. For example, old and new thread types (those that are being phased out and replaced), American, British, Whitworth, and national standards; sealing threads and connection threads; 55-degree and 60-degree threads. Really, no one can explain it clearly at once. Only one can be encountered at a time; check one first.
18G generally refers to the NPT thread of GB12716-2011 60° sealed pipe threads; it is an American standard thread and the one most commonly used in SH standards. The mainstream threads available on the market, and those most frequently used in daily applications, are GBT 7306.1-2000_55° sealed pipe threads_Part 1: Cylindrical male threads and tapered female threads, and GBT 7306.2-2000_55° sealed pipe threads_Part 2: Tapered male threads and tapered female threads. A standard 4-inch thread corresponds to 1/2 thread, which is 14G; a standard 6-inch thread corresponds to 3/4 thread, also 14G. As for whether it is a tapered or cylindrical thread, it can be determined from the designation such as R/RC/RP/G, etc
I roughly understand the basics of pipe threads, but I have a few questions: 1. What type of thread does “18G” on the thread gauge refer to? 55 degree unsealed G thread, 18 teeth per inch? Then why isn’t the pitch specified? 18G refers to 55-degree unsealed threads; the code G corresponds to standards such as ISO R226 and GB 7307. 18 refers to 18 teeth per inch, and it is used in this way to represent the pitch. For pitch gauges, the actual products I’ve studied also have markings such as 18G, 19G, 24G, etc.
Really? Isn’t the G thread a non-sealing pipe thread with a 55-degree angle?