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tapped plate rule of thumb

tapped plate rule of thumb

tapped plate rule of thumb

Hi All,

Is there a standard or a rule of thumb for the thickness of a plate to be welded to a structure that allows for a other framework to be bolted to it.
For instance lets say I have a PFC with and end plate welded to it with thru holes to accept a M14 screw. I want to mount this to an existing structure but want it removable so i want to weld a plate with tapped hole to the the structure. what thickness should this plate be to allow for the threaded connection? 15mm, 20mm?
many thanks

RE: tapped plate rule of thumb


The rule of thumb I always use is the thread engagement should be at least one bolt diameter but if the material is nothing like the strength of the bolt I would use 1.5 bolt diameter for my thread engagement.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: tapped plate rule of thumb

thank you i like that rule of thumb i will keep that in mind for my future applications..


RE: tapped plate rule of thumb

There are other options for one sided, removable connections too. Like Hollo-Bolt by Lindapter.

I've always been told to be careful about tapping plates for structural connections.

RE: tapped plate rule of thumb

The rule of thumb we use is the thickness of a nut for that size of fastener. That is, unless the fastener will be used as a pin used in shear rather than as a fastener loaded primarily in tension- then you can get away with much less thread engagement than that, as all the tapped thread is doing is keeping the fastener in place.

RE: tapped plate rule of thumb

True, but as desertfox already pointed out, a nut typically has a yield of 600+ MPa, whereas most structural steels that you'll tap only have a yield of about half of that (same applies for ksi values!).
Meaning you'll roughly need double the thread engagement! Which again does not add up with the fact that more than half of the tensile forces gets (re)distributed in the first 3 - 4 threads.

So, be careful using rules of thumb in soft or thin plates...

RE: tapped plate rule of thumb

Hi Jon

See this link, introductory notes it mentions the rule of thumb I quoted:-


“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

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