Blessed Bolts or Freaking Fasteners Or Bolt Basics!

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Bolts and screws are not something that occupies a lot of our reliability thoughts. After, the life of an appropriate bolt in a non-aggressive environment has been extrapolated to something like 11,000 years. Yet if you use the wrong fastener, it is bound to be very aggravating. It may not even survive its own virgin installation!

Luckily, there are some visual cues to help guide against using the wrong fastener. The following table shows grading of common US and Metric fasteners.

Maybe one day we will only have just the same system and less confusion. But you know the saying; “US is changing to the Metric standard inch by inch.” 

US Bolts (SAE J429)

Marking Grade Sizes Load (psi)* Strength (psi)**
image001 Grade 2 ¼” -3/4” 55,000 74,000
+3/4” – 1 ½” 33,000 60,000
Grade 5 ¼” – 1” 85,000 120,000
+1” – 1 ½” 74,000 105,000
clip_image004_0003.gif Grade 8 ¼” – 1 ½” 120,000 150,000

Metric Bolts (ISO R898)

Marking Grade Sizes Load (psi)* Strength (psi)**
clip_image001_0000.gif Class 4.6/ Class 5.8 1- 35mm 33,000/ 55,000 60,000/
74,000
image005.gif Class 8.8 Up to 16mm 84,000 116,000
16 – 72mm

87,000

120,000
image006_0002.gif Class 10.9 5 – 100mm 120,000 150,000
image001_0001.gif Class 12.9 1.6 – 100mm

141,000

177,000

*Load= Minimum load bolt must handle without permanent deformation.
**Strength (tensile)= Minimum load bolt must handle before braking or fracturing.

Michael Lippig

Michael Lippig

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