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I have noticed lately that there are "re-threading" tools being offered online but it they are not always a good thing to do.

Deleted the first text.

I made the post because what I am used to (Mil Spec fasteners and design limitations) design wise is not what is commercially readily available. Mil spec and commercially made fasteners are not necessarily made the same way (spec. wise) so interchangeability is not always a good thing to do due to strength differences.

I have seen "fixed" fasteners fail and re-tapping where they are to be used because of the changes made (e.g., not understanding limitations that are/were necessary.

Lee

Deleted.

Lee

https://www.bing.com/search?q=differenc ... c2b0d4e567

This might give some additional information that I may not have done well talking about in the past (deleted paragraphs or deleted) posts.

Cutting or reshaping of the (tired/worn) threads and the cutting into the material can cause the fasteners to get weak and fail. Commercial unlike mil-spec fasteners also does not seem to have cycle limitation use for example (a cycle is torque into place then remove then repeat the cycle.

The making of the threads on a bolt also changes the strength of the bolt. Threads can be either cut or rolled into shape with the rolled threads being the stronger. of the two. Threaded parts of the bolt are not designed to be available where the shear loading is being done. The shear loading part of the bolt is the "grip" part of the "shank" to handle.

Commercial fasteners also do not usually cover the "grade" definition of the strength of the fastener and mil-spec fasteners usually do.

For example: torquing the bolt in place stretches the bolt and locks it in position, then when you remove it, it shrinks back but some strength could be lost hence the limitations on cycles.

Lee