GD&T modifiers |F and |F/C

[CoryPad]

I have a drawing for a casting made from spheroidal graphite iron (also known as ductile or nodular). Some of the dimensions have modifiers like |F and |F/C. See image below.

What do these represent?

 

[KENAT]

Do you have datums F & C?

Did someone not know how to generate F-C in the FCF their CAD package or something?

In fact, a number of the call outs look odd in various ways so I'm wondering if someone that didn't know GD&T &/or the relevant CAD system did the drawing.

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[CoryPad]

Yes to datum C but no to datum F. It is drawn to ISO standards by a German-language company. I believe the rounded rectangles surrounding the dimensions are related to key characteristics that require statistical verification.

 

[CheckerHater]

The obround frames appear as infamous SolidWorks "critical dimension" symbols.

The numbers on the very right (4, 6) are probably references to QC sheet / inspection report.

Given the difference in accuracy between DIA 85 and DIA 80.5 (M6 vs. H6) one may speculate F and F/C means something like "Forged" / "Forged/Cut" but that just my imagination.

The appropriate ISO standard for castings is ISO 8062 (old 1994 or new 2008 parts 1, 2, 3). Something tells me you won't find F / F/C in there.

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[KENAT]

OK, does the F stand for Fine or similar, perhaps to ISO2768 or similar?

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[CheckerHater]

Found something: letters B thru K are used to indicate required machining allowance grade, BUT they should be used in general note and not the individual dimensions.

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