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USA & METRIC THREAD STANDARDS

Metric thread sizes are specified differently than USA thread sizes. USA sizes are specified using the nominal major diameter and the number of threads per inch. For example, a 3/8-16 (coarse) thread has a 3/8" nominal major diameter and 16 threads per inch, while a 3/8-24 (fine) thread has the same nominal major diameter and 24 threads per inch.

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

To simplify metric thread callouts, the international (ISO) standard for metric threads eliminates the pitch callout on coarse threads. For example, the thread "M10" automatically means a coarse pitch, while any added pitch callout, such as M10x1.25, specifies a non-coarse pitch. This method of designation has the major benefit that average citizens do not need to memorize pitches just to identify a coarse thread.

Virtually all thread standards across the world use the ISO designation convention, including the German DIN and Japanese JIS standards. All except the ANSI standard, which so far still asks for a pitch callout on coarse threads, despite the confusion that it causes.

Since Carr Lane does business all across the world, we follow the international (ISO) standard for metric thread callouts. Stating the pitch of a metric coarse thread would be incorrect and totally confusing everywhere else in the world. The following table shows the ANSI equivalent callout for each ISO thread size.

ISO Thread Designation

ANSI Equivalent

M1.6 M1.6x0.35
M2 M2x0.4
M2.5 M2.5x0.45
M3 M3x0.5
M3.5 M3.5x0.6
M4 M4x0.7
M5 M5x0.8
M6 M6x1
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
M42 M42x4.5
M48 M48x5
M56 M56x5.5
M64 M64x6
M72 M72x6
M80 M80x6
M90 M90x6
M100 M100x6

Carr Lane Manufacturing Co.
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