Letter 31694

How much thickness should I allow for plating? [No. Carolina] 

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What is the typical thickness for Zinc Plating F70B4A? We are a precision metal manufacturer and have a requirement for a pitch diameter of a threaded component to be made "snug to No-Go for acceptance after plating"; however, my no-go gage will not go on even snugly. I've measured the actual pitch diameter and would like to not have a rework process. The thread is 1 3/16-24.

Elizabeth McClellan
- Morganton, NC, USA

External threads. Reduce the minimum pitch diameter by not more than .001 inch on all threads for which the tolerance specified does not exceed .0035 inch. For threads with the pitch diameter tolerance greater than .0035 inch, the minimum pitch diameter may be reduced by an amount equal to 0.3 times the pitch diameter tolerance, but not more than .0015 inch.

Zinc plating will not normally "throw" into internal threads unless the diameter is .750 or larger or special probes are utilized. The same calculation can be used for internal threads.

Thomas J Luniewski
- Minneapolis, MN, USA

I don' t know the specifics on that spec. Typically zinc plating is about .0003 in. thick. That means you will have to allow .0006 in. on the diameter.

Todd Osmolski Charlotte Plating, Inc. Charlotte, NC USA

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Ed. note: The following letters also seem to offer insight into thread allowances for plated parts: 2906, 22409.

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