How much weight can a bolt take before the threads pull out?

Click For Summary

Discussion Overview

The discussion centers around determining the pull-out strength of bolts in threaded applications, specifically how to calculate the weight a bolt can support before the threads fail. Participants explore theoretical and practical aspects of this topic, including material properties and engagement lengths.

Discussion Character

  • Technical explanation, Exploratory, Homework-related

Main Points Raised

  • One participant suggests calculating the shear area and multiplying it by the shear strength of the softer material in the joint to estimate pull-out strength.
  • Another participant emphasizes the importance of determining which component (internal or external thread) is stronger to correctly identify the shear diameter for calculations.
  • It is noted that a length of engagement of at least 1.5 times the nominal diameter of the thread is generally sufficient to prevent thread pull-out, although this is contingent on the materials used.
  • A participant provides links to resources and calculators on Engineer's Edge that may assist in further understanding and calculations related to bolt strength.
  • Another participant recommends MIL-HDBK-60 as a useful reference for this topic.

Areas of Agreement / Disagreement

Participants generally agree on the methods for estimating pull-out strength but do not reach a consensus on specific formulas or the best resources to use. There are multiple approaches and considerations presented without a definitive resolution.

Contextual Notes

The discussion lacks specific assumptions about material properties and does not resolve the complexities involved in different materials and thread types. The effectiveness of the suggested methods may depend on various factors not fully explored in the conversation.

Spoolx
Messages
38
Reaction score
0
Hi All,
I was browsing the internet and came across this forum, I was thinking to myself one day and decided to do a google search.
My question is basically, how do I determine how much weight a bolt can take before it pulls out of the thread.

For example, I want to attach Part A to Part B with bolts and I am trying to determine the proper size. I am sure there is a formula that will tell me how much weight a bolt can take based on what material it is threaded in to, but I can't seem to find it.
I have my machinists handbook out but am having no luck, a point in the right direction would be much appreciated. I also have an old physics book and even if you could point me to the section of the book that deals with this concept, that would be appreciated also.

Thanks
Rich
 
Engineering news on Phys.org
Generally to determine pull out strength of a thread you will basically calculate the shear area (pi * shear diameter * length of engagement), and multiply by the shear strength of the softer component in the bolted joint.

You must decide which is the stronger material (or if they're both about the same)- the internal thread or external thread. If the internal thread (threaded hole) is stonger, your shear diameter should be about the minor diameter of the thread. If the external thread (bolt) is stronger, the shear diameter will be the major diameter of the thread. If both materials are about the same in terms of strength, use the pitch diameter of the thread.

This is a quick estimate, so make sure and build some safety factor in there as well. Generally as long as your length of engagement is >= 1.5x the nominal diameter of the thread, the fastener will snap before the threads pull out. However this is dependent on the materials being used.
 
thanks a bunch guys
 
MIL-HDBK-60 is good place to start.
 

Similar threads

Help me understand how bolts take less load than members
  • · Replies 5 ·
Replies
5
Views
2K
Forces applied on the bolts in the bike's hinge
  • · Replies 36 ·
2
Replies
36
Views
4K
Reusability of nuts and tapped holes + Choosing the right material
  • · Replies 3 ·
Replies
3
Views
2K
Minimum screw thread engagement to support weight?
  • · Replies 11 ·
Replies
11
Views
4K
Undergrad Understanding Bolted Joints: Shigley's Explanation & Real-Life Testing
  • · Replies 8 ·
Replies
8
Views
5K
Determine how many bolts are needed to secure a block of steel
  • · Replies 1 ·
Replies
1
Views
2K
Determine the strength of a Bolt-Nut combination
  • · Replies 12 ·
Replies
12
Views
5K
How much should I adjust torque when using anti-seize?
  • · Replies 22 ·
Replies
22
Views
7K
Bursting strength and compressive strength of cardboard tubes
  • · Replies 3 ·
Replies
3
Views
3K
How to Calculate Weight Transfer for Uprighting Vehicles with a Rotator Wrecker?
  • · Replies 9 ·
Replies
9
Views
2K