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this is the first time I'm making a PCB layout, so I'm not too familiar with datasheets. The picture below shows a diagram for an IC I'm using. The datasheet says all dimensions are in mm. However, near the bottom you can see a number that has 0.25 with a circled M, followed by an A and C. What do these letters mean? And does that mean the hole size is 0.25 mm for a pin? I'm really confused because I know it can't be 0.25mm. Is that in mils instead?

enter image description here

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  • \$\begingroup\$ Circled M = MMC = Maximum Material Condition \$\endgroup\$ – Spehro Pefhany Jul 14 '18 at 21:19
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You can read more about those symbols in this Drafting Manual but those particular symbols are related to the tolerance rather than size:

Tolerance symbols

It seems to me the seven pins have a diameter of 0.6 mm +/- 0.1mm with a spacing of 1.27 mm between them. It's quite common for dimensions to be prefixed by "7 x" etc to indicate the same dimension applies to multiple items.

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