I am sending my design for machining. In my design I am trying to assemble two metal parts with each other. In these holes I will be using m3 socket head bolt. I am confused what tolerance value should I put in the diameter of the hole.

Can anyone tell me how to calculate the tolerance for the diameter of the holes that will use standard screws such as m3/m6.

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1 Answer 1


IF I understand your question correctly what you are looking for is the clearance hole diameter. I.e. how big to make the hole to be able to let an M3 bolt to pass through.

you can find a lot of tables like the following in the internet, where you can see that the clearance hole is between 3.2 and 3.9 mm depending on the fit that want to have.

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  • $\begingroup$ Sir what should I search for this tolerance chart. $\endgroup$ Commented Aug 3, 2021 at 4:58
  • $\begingroup$ For most purposes I would just look at Medium fit, and I would select 3.4 and 3.58. $\endgroup$
    – NMech
    Commented Aug 3, 2021 at 5:03

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