Metric Fasteners — Metric Bolts, Standards & Sizes

What metric means for fasteners

A metric fastener is specified as M plus the nominal diameter in millimetres.

The metric designation states the nominal thread diameter directly in millimetres. M14 means a 14 mm nominal diameter; M6 means 6 mm. Everything else — pitch, head width, head height, length — follows from the standard the size belongs to.

The metric standards in this library are recorded with the coarse thread series (metric_coarse in the relationship file), which is the default series for general engineering work.

Metric standards in this library

All 12 metric standards, with the size range each one actually covers in this data source.

Standard	Category	Product	Size range	Sizes
DIN 931	BOLTS	Partial Thread Hexagon Head Bolt	M6 - M64	17
DIN 933	BOLTS	Full Thread Hexagon Head Bolt	M6 - M64	22
ISO 4014	BOLTS	Partial Thread Hexagon Head Bolt	M6 - M64	17
ISO 4017	BOLTS	Full Thread Hexagon Head Bolt	M6 - M64	22
DIN 934	NUTS	Hexagon Nut	M6 - M64	22
ISO 4032	NUTS	Hexagon Nut	M6 - M64	22
DIN 912	SCREWS	Socket Head Cap Screw	M6 - M6	1
ISO 4762	SCREWS	Socket Head Cap Screw	M6 - M6	1
DIN 125-A	WASHERS	Flat Washer	M6 - M36	19
DIN 127-A	WASHERS	Spring Lock Washer	M6 - M100	27
DIN 7980	WASHERS	Spring Lock Washer	M6 - M48	16
ISO 7089	WASHERS	Flat Washer	M6 - M36	19

Metric size coverage

The metric size range this library actually covers.

Distinct metric size steps	Smallest	Largest
32	M6	M100

Size steps counted across the 12 metric standards, from the size values recorded in this library's data source. The hexagon head bolt standards cover the widest span.

DIN and ISO metric equivalents

The metric standards split into a DIN family and a directly equivalent ISO family.

Standard	Metric equivalent	Relationship	Confidence
DIN 125-A	ISO 7089	interchangeable	0.95
DIN 127-A	DIN 7980	interchangeable	0.90
DIN 912	ISO 4762	interchangeable	0.99
DIN 931	ISO 4014	interchangeable	0.98
DIN 933	ISO 4017	interchangeable	0.98
DIN 934	ISO 4032	interchangeable	0.98

Metric property classes

Metric fasteners are graded by property class rather than by a material name. The classes recorded against metric records in this library are 4.6, 5.6, 5.8, 8.8, 10.9 and 12.9 for steel, plus A2-70, A4-70 and A4-80 for stainless steel, and the nut classes 04, 05, 08, 10 and 12.

Class type	Classes recorded	Detail
Bolt property class	4.6, 5.6, 5.8, 8.8, 10.9, 12.9	Mechanical Properties
Nut property class	04, 05, 8, 10, 12	Mechanical Properties
Washer hardness	100HV, 140HV, 200HV, 300HV	Mechanical Properties
Stainless	A2-70, A4-70, A4-80	Fastener Materials

Metric compared with imperial

	Metric	Imperial (ASME)
Standards in this library	12	4
Designation	M plus nominal diameter in mm	Fractional inch (for example 1/2, 5/16)
Thread series	metric coarse	UNC

This guide links only the metric standards. The four imperial standards are indexed in /library/, and the metric-to-imperial comparison is carried by /engineering-center/ and Fastener Standards.