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I would like to know if there is a definite way to understand what kind of diameter is indicated on the dwg by just looking at a dwg. I work in a job profile where I need to add inspection points to these measurements and the device used to inspect it. Most times I get confused if its an internal diameter measurement (using a gauge pin) or an external diameter (using a micrometer). Recently there was a sectional drawing with a cylindrical figure inside and there was a diameter measurement with tolerance shown. I assumed it was an external diameter measured using micrometer. But was corrected that its an internal one to be measured by a gauge pin. Thanks, VRij

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    $\begingroup$ You should include figures to indicate the confusion. $\endgroup$ – r13 May 4 at 15:24
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    $\begingroup$ There's also usually a centerline of the part showing what edge is towards the interior, it sounds like you're working with poor drawings $\endgroup$ – jko May 4 at 15:55
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Usually internal dimensions have arrows pointing out and external dimensions with arrows pointing in.

But I find the dimensions obvious even when there are just angled lines marking the points as the figure or object makes it clear. Knowing first angle, third angle does help.

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