Interpreting QQ-N-290A

How does the QQ-N-290A specification apply to nickel plating, particularly in terms of the 0.75" ball restrictions and requirements?

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Q. My question is about QQ-N-290A. What exactly are the 0.75" ball restrictions or requirements as far as nickel plating is concerned? We are being held to a tight tolerance of 90 to 150 microinches on some very small parts and there are vast differences in opinion on what this rule means. The area being measured by cross section would never be touched by the ball because of the size of the part. What is your opinion on this? –S.A.

A. I thought it best to review my stained, old copy of QQ-N-290A before answering your question. My copy has a penciled note on it reminding me to order a copy of the newer B version (which I haven't done yet). Based on the rule, Class 1, Grade C, plating the required thickness would be 0.0010" thick with the tolerance you mentioned. The 0.75" ball does not come into play since it does not touch any of the surfaces.

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