General ISO Metric threads

ISO Metric Thread and Spanner Sizes (mm)

Thread	AF ISO	AF JAP	ISO Std.**	ISO Fine	JAP Std.	Tapp-C	Tapp-F
M4	7	~	0.7	0.5	~	3.30	3.50
M5	8	~	0.8	0.5	~	4.20	4.50
M6	10	~	1.0	0.75	~	5.00	5.20
M7	11	~	1.0	0.75	~	6.00	6.20
M8	13	12	1.25	1.0	1.25	6.80	7.00
M9	14	~	1.25	~	~	7.80	~
M10	17	14	1.5	1.25/1.0*	1.25	8.50	8.80
M12	19	~	1.75	1.25*	~	10.20	10.80
M14	22	~	2.00	1.50^/1.25*	~	12.00	12.50
M16	24	~	2.00	1.50	~	14.00	14.50
M18	27	~	2.00	1.50*	~	15.50	16.50

* Metric Spark Plugs

** ISO Coarse Pitch is 'Common Metric Standard'

^ T25/T3 wheel studs

AF = Across Flats (Spanner/Socket Size)

Tapp-C = Tapping Drill Size (ISO Coarse)

Tapp-F = Tapping Drill Size (ISO Fine)

NB. Do not exceed tapping drill size when 'drilling out' broken bolts/studs.
HSCO (cobalt) jobber drills make drilling out hard, heat hardened or rusty studs and bolts much easier.

For more extensive range of metric tapping drill sizes, look here:-

(Thanks to Stephen Henderson's Cutting Edge Designs page.)

Compiled by: HarryMann