What decrease in torque can be expected with a 3mm hex compared to a 4mm hex?

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Discussion Overview

The discussion centers on the expected decrease in maximum torque when using a 3mm hex compared to a 4mm hex for set screws. Participants are exploring the implications of this change without conducting physical tests, focusing on theoretical estimates and practical applications related to torque limiting devices.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant reports having conducted mechanical testing on a 4mm hex and seeks to understand the torque implications of switching to a 3mm hex, specifically asking for a percentage decrease in torque.
  • Another participant suggests using about 40% of the torque value from the 4mm hex when tightening the 3mm screw, but does not provide a basis for this estimate.
  • A subsequent post questions the reasoning behind the 40% figure, seeking clarification on how that percentage was determined.
  • A participant shares a link that may contain relevant information, though its content is not discussed in detail.

Areas of Agreement / Disagreement

There is no consensus on the percentage decrease in torque, as the suggestion of 40% is questioned and not substantiated. The discussion remains unresolved regarding the exact torque reduction expected.

Contextual Notes

The discussion lacks detailed assumptions about the relationship between hex size and torque capacity, and the specific conditions under which the 40% figure was derived are not provided.

sbbiomed
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I have done mechanical testing on a set screw with a 4mm hex and its driver. I now have a set screw with a 3mm hex. Without the time and expense of making parts and testing, I want to know the percentage decrease in maximum torque that the set screw and/or driver will be able to withstand on the 3mm hex. I am getting a torque limiting device and I need it to be used for both set screws and I don't want it to strip the hex on the 3mm driver by being too large of a value.

If the materials and hex depth do not change (only change is 4mm to 3mm hex), what decrease do I expect to see in the 3mm hex?

Thanks,
sbbiomed
 
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If I understand your question correctly, you should use about 40% of the 4 mm torque when tightening the 3 mm screw.
 
How did you get 40%

How did you get to 40%?
 

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