Thread pitch: Also known as screw pitch, refers to the axial distance between two corresponding points on the midline of adjacent threads, or the distance between adjacent crests or depressions.
The metric thread pitch is marked directly with the distance (in millimeters, mm). For example, in M8*1.25, 1.25 indicates that the thread pitch for M8 is 1.25MM.
Sometimes, out of habit, people tend to omit the thread pitch for commonly used metric threads such as M8, which implies that the thread pitch is 1.25MM by default.
However, it is best to avoid abbreviations to avoid unnecessary misunderstandings.
The thread pitch of a British or Imperial nut is marked by the number of threads contained within each inch.
For example, in 1/4-20, the 20 indicates that there are 20 threads per inch, which is approximately 1.27 mm in metric units.
However, it is not stated as 1.27. For standard threads with a diameter of less than 1/4 inch, the diameter is no longer indicated as a fraction such as “1/4”, but is indicated by the number, as seen in 10#-24, 8#-32, etc. .
Metric thread pitch standard table
(Including thick and thin wires)
Units are in millimeters (mm)
| Nominal diameter | Thread pitch (i.e. threads per inch) | |
| Coarse Threads (UNC) | Fine Lines (UNF) | |
| M1 | 0.25 | 0.2 |
| M1.2 | 0.25 | 0.2 |
| M1.6 | 0.35 | 0.2 |
| M2 | 0.4 | 0.25 |
| M2.5 | 0.45 | 0.35 |
| M3 | 0.5 | 0.35 |
| M3.5 | 0.6 | 0.35 |
| M4 | 0.7 | 0.5 |
| M5 | 0.8 | 0.5 |
| M6 | 1 | 0.75 |
| M8 | 1.25 | 1 |
| M10 | 1.5 | 1.25 |
| M12 | 1.75 | 1.25 |
| M14 | two | 1.5 |
| M16 | two | 1.5 |
| M18 | 2.5 | 1.5 |
| M20 | 2.5 | 1.5 |
| M22 | 2.5 | 1.5 |
| M24 | 3 | two |
| M27 | 3 | two |
| M30 | 3.5 | two |
| (M33) | 3.5 | two |
| M36 | 4 | 3 |
| (M39) | 4 | 3 |
| M42 | 4.5 | 3 |
| (M45) | 4.5 | 3 |
| M48 | 5 | 3 |
Imperial standard thread pitch table
(Including thick and thin wires)
| Nominal diameter | Diameter size | Thread pitch (i.e. threads per inch) | ||
| inch | mm | Coarse Threads (UNC) | Fine Lines (UNF) | |
| 0# | 0.06 | 1,524 | – | 80 |
| 1# | 0.073 | 1,854 | 64 | 72 |
| two# | 0.086 | 2,184 | 56 | 64 |
| 3# | 0.099 | 2,515 | 48 | 56 |
| 4# | 0.112 | 2,845 | 40 | 48 |
| 5# | 0.125 | 3,175 | 40 | 44 |
| 6# | 0.138 | 3,505 | 32 | 40 |
| 8# | 0.164 | 4,166 | 32 | 36 |
| 10# | 0.19 | 4,826 | 24 | 32 |
| 12# | 0.216 | 5,486 | 24 | 28 |
| 1/4″ | 0.25 | 6:35 am | 20 | 28 |
| 05/16″ | 0.3125 | 7,938 | 18 | 24 |
| 3/8″ | 0.375 | 9,525 | 16 | 24 |
| 7/16″ | 0.4375 | 11,113 | 14 | 20 |
| 1/2″ | 0.5 | 12.7 | 13 | 20 |
| 9/16″ | 0.5625 | 14,288 | 12 | 18 |
| 5/8″ | 0.625 | 15,875 | 11 | 18 |
| 3/4″ | 0.75 | 19.05 | 10 | 16 |
| 7/8″ | 0.875 | 22,225 | 9 | 14 |
| 1" | 1 | 25.4 | 8 | 12 |
| 1-1/8″ | 1,125 | 28,575 | 7 | 12 |
| 1-1/4″ | 1.25 | 31.75 | 7 | 12 |
| 1-3/8″ | 1,375 | 34,925 | 6 | 12 |
| 1-1/2″ | 1.5 | 38.1 | 6 | 12 |
| 1-3/4″ | 1.75 | 44.45 | 5 | – |
| two" | two | 50.8 | 4.5 | – |
