A simple chart to check the size of the pitch, both fine and coarse, of the most common metric and imperial threads.
Thread pitch - Metric ISO
The ISO metric thread represents the standard recognized by the International Organization for Standardization since 1947. It consists of a triangular profile thread with a 60° profile angle.
Screws with ISO metric threads are identified by an M followed by the nominal diameter in mm and, in the case of fine threads, by the thread pitch.
The thread pitch is the distance (in mm) between two consecutive threads of the same helix, along the longitudinal section of the thread.
Examples:
- Standard pitch (coarse), nominal diameter 8 mm: M8.
- Fine pitch thread, nominal diameter 10 mm pitch 0,75 mm: M10x0,75.
Note: the standard threads are always "coarse" since this pitch is the largest of those that ensure the seal against unscrewing; if you want to obtain an anti-unscrewing tightening it is necessary to use the standard pitch or finer pitches.
| THREAD PITCH | ||||
|---|---|---|---|---|
| DIAMETER | COARSE | FINE | ||
| M1 | 0.25 | 0.2 | ||
| M1.2 | 0.25 | 0.2 | ||
| M1.4 | 0.3 | 0.2 | ||
| M1.6 | 0.35 | 0.2 | ||
| M1.7 | 0.35 | |||
| M1.8 | 0.35 | 0.2 | ||
| M2 | 0.4 | 0.25 | ||
| M2.2 | 0.45 | 0.25 | ||
| M2.3 | 0.4 | |||
| M2.5 | 0.45 | 0.35 | ||
| M2.6 | 0.45 | |||
| 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 | ||
| M7 | 1 | 0.75 | ||
| M8 | 1.25 | 1 | 0.75 | |
| M9 | 1.25 | 1 | 0.75 | |
| M10 | 1.5 | 1.25 | 1 | 0.75 |
| M11 | 1.5 | 1 | 0.75 | |
| M12 | 1.75 | 1.5 | 1.25 | 1 |
| M14 | 2 | 1.5 | 1.25 | 1 |
| M16 | 2 | 1.5 | 1 | |
| M18 | 2.5 | 2 | 1.5 | 1 |
| M20 | 2.5 | 2 | 1.5 | 1 |
| M22 | 2.5 | 2 | 1.5 | 1 |
| M24 | 3 | 2 | 1.5 | 1 |
| M27 | 3 | 2 | 1.5 | 1 |
| M30 | 3.5 | 3 | 2 | 1.5 |
| M33 | 3.5 | 3 | 2 | 1.5 |
| M36 | 4 | 3 | 2 | 1.5 |
| M39 | 4 | 3 | 2 | 1.5 |
| M42 | 4.5 | 4 | 3 | 2 |
| M45 | 4.5 | 4 | 3 | 2 |
| M48 | 5 | 4 | 3 | 2 |
| M52 | 5 | 4 | 3 | 2 |
| M56 | 5.5 | 4 | 3 | 2 |
| M60 | 5.5 | 4 | 3 | 2 |
| M64 | 6 | 4 | 3 | 2 |
| M68 | 6 | 4 | 3 | 2 |
| M72 | 6 | 4 | 3 | 2 |
| M80 | 6 | 4 | 3 | 2 |
| M90 | 6 | 4 | 3 | 2 |
| M100 | 6 | 4 | 3 | 2 |
The fine pitch threads are available in different sizes for the same diameter, for example M100x4, M100x3 and M100x2.
Metric Pitch Threads Chart, Pdf File
Metric Pitch Threads Chart From M1 to M33, Jpeg File
Metric Pitch Threads Chart From M36 to M100, Jpeg File
Conversion chart Metric - Imperial
| FROM IMPERIAL TO METRIC | FROM METRIC TO IMPERIAL | ||
|---|---|---|---|
| 1 inch | 25.4 mm | 1 mm | 0.03937 inches |
| 1 inch | 2.54 cm | 1 cm | 0.3937 inches |
| 1 foot | 30.48 cm | 1 m | 3.2808 foots |
| 1 yard | 0.9144 m | 1 m | 1.0936 yard |
| 1 mile | 1.6093 Km | 1 Km | 0.62137 miles |
Thread pitch - Imperial (Whitworth)
The Whitworth thread, born in 1833, is the first standard threading project: it has two pitches, fine and coarse. It consists of a triangular profile thread with a profile angle of 55°.
For example, the 1 ½ "Whitworth thread is indicated: 1 ½ W, meaning therefore a standard pitch which for this dimension, by law, is 6 threads per inch.
The thread pitch is the distance (in mm) between two consecutive threads of the same helix, along the longitudinal section of the thread.
| DIAMETER | PITCH | THREADS PER INCH |
|---|---|---|
| 1/4" | 1,270 | 20 |
| 5/16" | 1,411 | 18 |
| 3/8" | 1,588 | 16 |
| 7/16" | 1,814 | 14 |
| 1/2" | 2,117 | 12 |
| 5/8" | 2,309 | 11 |
| 3/4" | 2,540 | 10 |
| 7/8" | 2,822 | 9 |
| 1" | 3,175 | 8 |
| 1.1/8" | 3,629 | 7 |
| 1.1/4" | 3,629 | 7 |
| 1.3/8" | 4,233 | 6 |
| 1.1/2" | 4,233 | 6 |
| 1.5/8" | 5,080 | 5 |
| 1.3/4" | 5,080 | 5 |
| 1.7/8" | 5,644 | 4 1/2 |
| 2" | 5,644 | 4 1/2 |
| 2.1/4" | 6,350 | 4 |
| 2.1/2" | 6,350 | 4 |
| 2.5/8" | 6,350 | 4 |
| 2.3/4" | 7,257 | 3 1/2 |
| 3" | 7,257 | 3 1/2 |
| 3.1/4" | 7,815 | 3 1/4 |
| 3.1/2" | 7,815 | 3 1/4 |
| 3.3/4" | 8,467 | 3 |
| 4" | 8,467 | 3 |
| 4.1/4" | 8,835 | 2 7/8 |
| 4.1/2" | 8,835 | 2 7/8 |
| 4.3/4" | 9,236 | 2 3/4 |
| 5" | 9,236 | 2 3/4 |
| 4.1/4" | 9,676 | 2 5/8 |
| 5.1/2" | 9,676 | 2 5/8 |
| 5.3/4" | 10,160 | 2 1/2 |
| 6" | 10,160 | 2 1/2 |
How to measure the thread pitch
When you need to measure an undefined thread pitch you need a specific tool called pitch gauge.
The thread pitch gauge consists of a series of blades, each of which is shaped to fit perfectly on the crests of the thread of your screw or nut.
It is important to know that there are different types of threads, therefore a single diameter can be threaded in various ways, the thread counter exists precisely to identify the type and the pitch of a specific thread.
A thread pitch gauge is called "simple" if include the pitches of only one type of thread, double if include two types of thread, for example metric on one side and imperial (Whitworth) on the other.
The measurement with the thread pitch gauge takes place by trial and error, looking for which lamina fits the thread of the screw. Once the right lamina is found, the pitch size can be read on the lamina itself.
It might interest you:
Size Chart For Bolts - Standard and Metric