Metric Screw Threads

In 1898 an international congress held at Zurich (the Congrès International pour l'Unification des Filetages) adopted a thread form similar to the United States Standard thread, except that the roots were rounded. The French had their own SI series.

Major Diameter in millimeters				Pitch (distance from thread to thread) in millimeters
ISO 1st pref.	ISO 2nd pref.	ISO 3rd pref.	Non- ISO	ISO Coarse	ISO Fine	SI Fine	SI coarse	JIS	DIN Fine	DIN Standard
1				0.25	0.2	0.2	0.25		0.20
	1.1			0.25	0.2
1.2				0.25	0.2	0.2	0.25		0.20
	1.4			0.30	0.2	0.2	0.3		0.20
1.6				0.35	0.2
			1.7			0.2	0.35		0.20
	1.8			0.35	0.25
2				0.40		0.25	0.4		0.20
	2.2			0.45	0.35
			2.3			0.25	0.4		0.25
2.5				0.45	0.35
			2.6			0.35	0.45		0.25
3				0.5	0.35	0.35	0.5	0.6	0.35	0.5
	3.5				0.35	0.35	0.6		0.35
4				0.70	0.5	0.5	0.7	0.75	0.35	0.7
	4.5				0.5	0.5	0.75		0.5
5				0.80	0.5	0.5	0.8	0.9	0.5	0.8
		5.5			0.5
6				1.00	0.75	0.75	1	1	0.75	1
	7			1.00	0.75	0.75	1
8				1.25	1	1	1.25	1.25	1.0	1.25
		9		1.25		1	1.25
10				1.5	1.25	1	1.5	1.25	1.0	1.5
		11		1.5
12				1.75	1.25	1.5	1.75	1.5	1.5	1.75
	14			2.0	1.5	1.5	2	1.5	1.5	2.0
		15
	16			2.0	1.5	1.5	2	1.5	1.5	2.0
		17
	18			2.5	1.5	1.5	2.5			2.5
20				2.5	1.5	1.5	2.5			2.5
	22			2.5	1.5	1.5	2.5			2.5
24				3.0	2.0	2	3			3
		25
		26
	27			3.0		2	3			3
		28
30				3.5		2	3.5			3.5

Metric Screw Thread Series

to 30 mm diameter