Your Guide to Metric Fasteners

The vast majority of metric fasteners are made to DIN (deutsches Institut für Normung) otherwise known as the German Institute for standards. This standard, created long before ISO (International Organization for Standardization), has DIN standards for almost everything.

Thread Pitch

-Metric bolts are identified by the capital letter “M” followed by the nominal diameter, thread pitch & length (in millimeters)

EXAMPLE: M10 X 1.5 X 25 = 10MM DIAMETER X 1.5 THREAD PITCH X 25MM LONG

-If no thread pitch is defined, it is assumed to be coarse thread

-Metric thread pitch is the distance from the crest of the thread to the crest of the next thread 

Click HERE to find our easy-read Metric and SAE thread pitch identification charts

Fastener Markings

What do the markings on the head of fasteners indicate?

When it comes to Metric fasteners, there are usually 2 indications:

1. Manufacturers marking
2. Strength class, which consists of two numbers separated by a decimal point
3. Common classes are:
   1. 4.8
   1. 8.8
   1. 10.9
   1. 12.9
4. The number on the left indicates that 1% of tensile strength in MPA or N/mm²
5. The number on the right indicates the proportion of yield strength in relation to tensile strength

Example

Example for Class 12.9

Left Digit 12 (Tensile Strength)	Right Digit .9 (Yield Strength)
12 x 100 = 1200 MPa = 1200 N/mm2	.9 x 1200 = 1080 MPa = 1080 N/mm2
Conversion factor for psi = 145	Conversion factor for psi = 145
1200 MPa x 145 = 174000 psi	1080 MPa x 145 = 156600 psi