The situation with pipes is as follows: most pipes twist and unwind normally. But every 5-7 pipe has a thread problem. These pipes are difficult to twist, they need to be wrapped with great effort while gently tapping on the thread with a hammer. With this method, the client succeeds in twisting the pipes to the end, but then they unwind just as hard. There are pipes that cannot be screwed to the end; the client puts such pipes aside and does not use them. There are 8 such pipes for today.