Inch and Metric Thread Chart: Understanding Thread Sizes

Metric thread sizes are specified differently than inch thread sizes. Inch sizes are determined using the nominal major diameter and the number of threads per inch.

For example, a 3/8-16 (coarse) thread has a nominal major diameter of 3/8" and 16 threads per inch.


Understanding the explanations of inch and metric spirals

Metric thread explanations are fundamentally different because the thread pitch is specified instead of threads per inch or per mm. The spiral pitch is the distance between each spiral in mm. For example, an M10x1.5 (coarse) thread has a pitch of 1.5 mm, while an M10x1.25 (fine) thread has a pitch of 1.25 mm.

To simplify metric thread callouts, the International Standard (ISO) for metric threads eliminates the callout on coarse threads.

For example, "M10" thread automatically means coarse pitch, while each additional feed pitch, such as M10x1.25, specifies a non-coarse pitch. The ISO standard for measuring coil sizes eliminates the need to memorize forward messages. This makes it more affordable for average citizens.

Using this method, what does the designation M16x2 indicate? According to ISO standards, the pitch legend is removed because the thread type is coarse, so M16x2 is designated as "M16".


ANSI equivalent for ISO thread sizes

Almost all body standards around the world adhere to ISO designation contracts, including the German DIN and Japanese JIS standards. However, the ANSI standard does not and calls for a pitch callout on coarse threads.

Since Carr Lane Mfg. operates around the world, we follow the international standard (ISO) for metric thread promotions. The statement of the height of a metric coarse spiral that was wrong and completely confused by another in the world. The following table shows the equivalent ANSI message for each ISO coil size.


What is the difference between metric and inch threads?

Metric coils are defined as the distance between each coil in millimeters (mm). While inch coils are the measure of the distance between each coil in inches.


Inch and Metric Coil Conversion Chart

The table below compares the ISO thread designation with the ANSI equivalent.


ISO THREAD DESIGNATIONANSI EQUIVALENT
M1.6M1.6x0.35
M2M2x0.4
M2.5M2.5x0.45
M3M3x0.5
M3.5M3.5x0.6
M4M4x0.7
M5M5x0.8
M6M6x1
M8
M8x1		M8x1.25
M8x1
M10
M10x1.25		M10x1.5
M10x1.25
M12
M12x1.25		M12x1.75
M12x1.25
M14
M14x1.5		M14x2
M14x1.5
M16
M16x1.5		M16x2
M16x1.5
M18
M18x1.5		M18x2.5
M18x1.5
M20
M20x1.5		M20x2.5
M20x1.5
M22
M22x1.5		M22x2.5
M22x1.5
M24
M24x2		M24x3
M24x2
M27
M27x2		M27x3
M27x2
M30
M30x2		M30x3.5
M30x2
M33
M33x2		M33x3.5
M33x2
M36
M36x3		M36x4
M36x3
M42M42x4.5
M48M48x5
M56M56x5.5
M64M64x6
M72M72x6
M80M80x6
M90M90x6
M100M100x6

 



Source: https://www.carrlane.com/engineering-resources/technical-information/design-standards-and-engineering-information/inch-and-metric-thread-standards