**12.9**grade steel

**means**that a component manufactured form this grade of steel has 12X100 N/mm^2 tensile strength and 9

**is**a multiplier

**means**90% of 1200 = 1080 N/mm^2

**is**the yield strength of the grade. Similarly we also have grade 8.8 , 10.9 , 6.8 also.

Also to know is, what is a 8.8 Bolt?

The first digit relates to the ultimate strength of the material, whilst the second is the ratio of yield stress to ultimate strength. Thus grade 4.6

**bolts**have an ultimate material strength of 400N/mm2 and the uield (or proof) stress is 60% of the ultimate strength.What size is a 8.8 Bolt?

Bolt Grade Markings and Strength Chart

Grade and Material | Nominal Size Range (inches) |
---|---|

Class 8.8 Medium carbon steel, quenched and tempered | 16mm - 72mm |

Class 10.9 Alloy steel, quenched and tempered | 5mm - 100mm |

Class 12.9 Alloy steel, quenched and tempered | 1.6mm - 100mm |

What is a metric bolt?

The size of a

**metric screw**or**bolt**is specified as diameter, pitch and length, in millimeters (millimeters is abbreviated "mm"). If you need to know the threads per inch of a**metric**fastener, first convert pitch from millimeters to inches (multiply by 0.03937), then divide 1 by that number.