Metrics in Engineering - ISO Metric Threads and Tapping Sizes

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Metric Threads

There are two kinds of ISO metric threads: coarse and fine.

The ISO metric thread profile and proportions are as follows:

Metric Thread Pitch and Tapping Sizes

Size	Pitch (mm)		Tapping Diameter (mm)		Clearance Holes (mm)
	Coarse	Fine	Coarse	Fine	Close	Medium	Coarse
M1.6	0.35		1.25		1.7	1.8	2.0
M2	0.4		1.6		2.2	2.4	2.6
M2.5	0.45		2.05		2.7	2.9	3.1
M3	0.5		2.5		3.2	3.4	3.6
M4	0.7		3.3		4.3	4.5	4.8
M5	0.8		4.2		5.3	5.5	5.8
M6	1.0		5.0		6.4	6.6	7.0
M8	1.25	1.0	6.8	7.0	8.4	9.0	10.0
M10	1.5	1.25	8.5	8.7	10.5	11.0	12.0
M12	1.75	1.25	10.2	10.8	13	14	15
M16	2.0	1.5	14.0	14.5	17.0	18.0	19.0
M20	2.5	1.5	17.5	18.5	21.0	22.0	24.0
M24	3.0	2.0	21.0	22.0	25.0	26.0	28.0
M30	3.5	2.0	26.5	28.0	31.0	33.0	35.0
M36	4.0	3.0	32.0	33.0	37.0	39.0	42.0