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The Anatomy of a Fastener

Designing fastened joints begins with a good basic knowledge of fasteners. Many engineers think they know enough about fasteners to make good decisions, but what is your level of knowledge? Here is some good information with questions at the end to test your knowledge:

Drive Styles

What is the difference between the Philips drive and the Pozidrive?

  • Applying too much torque to a Philips drive will cause it to “cam out” to avoid breaking the screw. This is beneficial for certain hand assemblies by consumers. For production assembly, it is not ideal due to tooling wear and operator fatigue if assembling by hand.
  • Pozidrive has different geometry which transfers more torque into the screw with less downforce. In a production environment, whether by hand or automated assembly, tooling will last longer and achieving a specific torque without the drive slipping is possible.

How do you tell the difference?

Pozidriv has four “tick marks” on the face of the drive for identification.

Do they use the same driver?

Property Class/Grade

How do you determine the strength of a fastener by looking at the head?

The grade or property class marks are on the head.

  • Left – property class 8.8 metric with the “8.8” stamped on the head
  • Middle – three slash marks equally spaced is imperial grade 5, which is the same strength as metric property class 8.8
  • Right – six slash marks equally spaced is imperial grade 8 which is stronger than grade 5

What does the triangle and the “ABCD” mean on the head? What does 8.8 stand for on the head of the metric fastener? What is the grade of fasteners below?

To check your answers to the questions above, contact us at ProvenProductivity@bossard.com to set-up a seminar at your facility, or keep your eyes open for our first webinar covering “The Anatomy of a Fastener”.

More than the basics, this seminar takes things to the next level by covering bolted joint principles and fastener manufacturing.

Doug Jones
Applications Engineer
djones@bossard.com

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May 24, 2019

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