Position tolerance

Does position tolerance is only applicable for holes? Recently I saw a diagram in which position tolerance was mention for a curved surface...can any one help me to clear this doubt.....

Thanks in advance.

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1 Answer

Position is used to control "features of size". Holes, bosses, slots, walls...if you can place imaginary (or real) calipers across opposing surfaces and measure their width, you can control the location of the center-plane or axis of that feature with position.

The tolerance zone of circular features of size is a cylinder of the size specified in the position callout. These must have a diameter symbol in the callout.

The tolerance zone of non-circular features of size are two parallel planes, distance between them equal to the callout, centered on the nominal or "basic" location dimension. These must not have a diameter symbol in the callout.

Position tolerance on a single curved surface like the hood of a car for example, would not be appropriate, profile of a surface should be used in that case.

You get bonus points for not calling it "true position", by the way ;-)

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