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screw threads
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Posted by: rrunge3

08/17/2004, 13:59:03

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Hello, I have a question regarding screw threads. What is the difference between 2A and 3A threads? I have a drawing that calls out a 3B nut with a 2A screw. I am trying to find out if this is OK as is or if it needs to be changed. I was oncle told (for example) that the 1, 2, 3, relates to a tolerance. Which one is tighter, I don't know. So in that thinking, a 2A male thread would be OK into a 3B female thread. Am I thinking right here? Like male 2s can mesh with female 3s, but female 3s would not go with male 2As, because the tolerance is tighter.

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thread tolerance factors
Re: screw threads -- rrunge3 Post Reply Top of thread Forum
Posted by: randykimball
08/17/2004, 20:57:09

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Male thread: The larger the number (1, 2, 3) the larger the pitch diameter and the closer the tolerance. example 1; 1/4-20 UNC Pitch diameter tolerance: 1A .2164 / .2108, 2A .2164 / .2127, 3A .2175 / .2147.

Female thread: The larger the number (1, 2, 3) the smaller and tighter the larger end of the tolerance factor. The small end of the tolerance does not change. example 2; 1/4-20 UNC - Pitch diameter tolerances: 1B .2175 / .2248, 2B .2175 / .2223, 3B .2175 / .2211.


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Modified by randykimball at Tue, Aug 17, 2004, 21:01:29

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