BẢNG TRA KÍCH THƯỚC REN HỆ INCH -TIÊU CHUẨN NPT (NORMAL PIPE THREAD)
| Nominal Diameter | Major Diameter | Tapping | TPI | Pitch | |
| 1/16" - 27 NPT | 7.895 | 6.00 | 27 | 0.941 | |
| 1/8" - 27 NPT | 10.242 | 8.25 | 27 | 0.941 | |
| 1/4" - 18 NPT | 13.616 | 10.70 | 18 | 1.411 | |
| 3/8" - 18 NPT | 17.055 | 14.10 | 18 | 1.411 | |
| 1/2" - 14 NPT | 21.223 | 17.40 | 14 | 1.814 | |
| 3/4" - 14 NPT | 26.568 | 22.60 | 14 | 1.814 | |
| 1" - 11 1/2 NPT | 33.228 | 28.50 | 11.5 | 2.209 | |
| 1 1/4" - 11 1/2 NPT | 41.985 | 37.00 | 11.5 | 2.209 | |
| 1 1/2" - 11 1/2 NPT | 48.054 | 43.50 | 11.5 | 2.209 | |
| 2" - 11 1/2 NPT | 60.092 | 55.00 | 11.5 | 2.209 | |
| 2 1/2" - 8 NPT | 72.699 | 65.50 | 8 | 3.175 | |
| 3" - 8 NPT | 88.608 | 81.50 | 8 | 3.175 | |
| 3 1/2" - 8 NPT | 101.316 | 94.30 | 8 | 3.175 | |
| 4" - 8 NPT | 113.973 | 107.00 | 8 | 3.175 | |
| 5" - 8 NPT | 141.300 | 134.384 | 8 | 3.175 | |
| 6" - 8 NPT | 168.275 | 161.191 | 8 | 3.175 | |
| 8" - 8 NPT | 219.075 | 211.673 | 8 | 3.175 | |
| 10" - 8 NPT | 273.050 | 265.311 | 8 | 3.175 | |
| 12" - 8 NPT | 323.850 | 315.793 | 8 | 3.175 | |
