# 12.9 Bolt Shear Capacity

by Bob WhiteNuts and bolts are the glue that hold together our mechanical contraptions. These simple devices are one of the most important inventions of the mechanical age. The 12.9 bolt is a higher tensile bolt made from alloy steel that is quenched and tempered. They are commonly used at high stress points in connecting devices.

### 12.9 Bolts

A 12.9 bolt is one of the highest grade of bolts produced. Known for their high tensile strength, they are built with both hex and Torx heads and are available in zinc or chrome finishes. A 12.9 bolt is tightened with a torque wrench to 90 percent of its proof load. Because of their hardened surfaces, lock washers are ineffective because they can't bite into the metal.

### MPa

The strength of a 12.9 bolt is rated in MPa, or megapascals. A Megapascal is equal to one million pascals. A pascal is a unit of pressure that is equal to one newton of force applied over an area of one square meter. A newton (N) is a measurement of force relative to gravity. One newton is equal to the force required to accelerate one kilogram, at a speed of one meter per second.

### Shear Strength

The shear strength of a bolt is a measurement of the minimum amount of force needed to break the bolt into two pieces. The shear strength of a metal bolt is approximately 0.6 times its tensile strength. A bolt commonly shears where its head meets the threads.

### 12.9 Shear Strength

The minimum tensile strength of a 12.9 bolt is 1220 MPa. Therefore, the approximate shear strength of a 12.9 bolt is 732 MPa. The minimum yield strength of a bolt is the pressures needed to stretch the metal of the bolt. A 12.9 bolt has a minimum yield strength of 1100 MPa.

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