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Metric Bolt Torque Specs

Metric Bolts With Head Markings

Like bolts from the Society of Automotive Engineers (SAE), metric bolts have specific torque values according to the grade of metal (measured by the amount of carbon in it) and diameter of the bolt. These bolts commonly come in "low grade," "8.8," "10.9", and "12.9."

Markings are usually on the bolt head itself or underneath the head on the shaft or underside of the bolt head. If no markings are present, assuming it is a low grade bolt.

We discussed metric grade and torque values in our Metric Bolt Chart, reproduced below.

Metric Bolts
Maximum Torque in ft lbs for clean, dry threads
Bolt Size Low Grade Grade 8.8 Grade 10.9 Grade 12.9
6mm 3-5lb 7lb 10lb 12lb
8mm 8-12lb 17lb 24lb 29lb
10mm 15-22lb 33lb 47lb 57lb
12mm 39lb 59lb 83lb 100lb
14mm 60lb 101lb 131lb 158lb
16mm 60-94lb 146lb 202lb 247lb
18mm 60-130lb 201lb 283lb 340lb
20mm 166-188lb 285 lb 401lb 482lb

Although this chart is not definitive and should be over-ridden by any shop manuals or application-specific information, it gives a base outline of the torque values recommended for bolts in grades and diameter.

Bolts are commonly tested in one or more ways. Tensile strength is determined by the maximum load (pulling) that the material can withstand before breaking or fracturing.

Yield Strength is the maximum load a material can stand before exhibiting a specific, permanent deformation.

Proof Load is the axial tensile load that a product must be able to withstand without evidence of any permanent set.

Most quality manufacturers test with all three measurements on random lots of their production line. Some specifications for critical designs will require a Proof Load on all bolts being used.

Related Articles

Torque Specs for Bolts

Torque Specification

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