Same size to manufacture internal threads and external threads ?
No. It is same with a phenomena that a cylinder of just 6 mm dia. never enters into a hole of just 6 mm dia. Although the size is same, we have to manufacture the internal thread and the external threads by using different sizes. For example, in the case of screw thread M6 x 1, following is the actual specification ( Accuracy is JIS 2nd class.) . Unit is millimeter. Basic size: Major diameter 6.000, Pitch diameter 5.350, Minor diameter 4.917. Size of external threads: Major diameter 5.970 ~ 5.820, Pitch diameter 5.320 ~ 5.220, Minor diameter 4.743 ~ Size of internal threads: Major diameter not specified (but for larger than 6), Pitch diameter 5.470 ~ 5.350, Minor diameter 5.153 ~ 4.917 Major diameter of external thread meets with that of internal thread, and minor diameter of external thread meets with that of internal thread. So the sizes of internal threads prove to be slightly larger than those of external threads. Usually external threads are smaller than the basic sizes and intern
