partially opposed FOS 1

[bxbzq]

There has been a lot of discussion on FOS in this forum. I don't intend to stir the pot here but I don't find answer to this question. See attached sketch. For two partially opposed planar surfaces being directly toleranced by 80±1, is there an agreement that the full planar surfaces are part of FOS? I'm asking because I also heard in this case the FOS ends where the opposed elements end, meaning the areas outside of the 30mm length (non-opposed portions) are not part of FOS.

 

[fsincox]

Jim,
I have the 1966, 1973, 1982, 1994 & 2009 versions and I suspect the caliper rule is like the "expansion of +/- tolerance to cylindrical tolerance value graph", something that is often touted in all the books of its proponents, but never really officially part of the standard itself. Someone please correct me if I missed it.
"FOS" receives a passing mention as part of "rule number 1" but as a defined term, itself, it is not even in the index until the 1982 version. I think those "outside the beltline", like myself before I came here, could easily miss the importance we all, now, seem to put on its distinction.

 

[MechNorth]

Could well be, Frank. I was shown the caliper rule in a standard some time ago, but I honestly don't remember what book it was from.

Jim Sykes, P.Eng, GDTP-S
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