For many years now I have observed that component data sheets are often in error when it comes to physical dimensions. There are probably several reasons why this happens. The part is designed in one system of measure and the conversion is done by another, less skilled person so it is not exact. Sometimes there are rounding errors. An exact conversion or even an exact number in the same units used for the design process has too many decimal places so some are just omitted. Then there is the tolerance range. It seems like in this case a number representing the low end of the tolerance range was used.
Two things to keep in mind: first, electrical engineers are not mechanical engineers. Yes, they should understand these things, but … And second, the task of publishing the specifications may not be done by the design engineer. It may be handed off to a less skilled employee. A MUCH LESS SKILLED one. They cost less for their time.
It is a real world. If a physical dimension does not seem to be an even number in either the English or the metric system, perhaps it should be double checked. That’s my rule and it has saved me on many occasions. In today’s world, most parts can be in your hands in a day or two. I don’t like ordering PCBs before I can make a full size paper print and assemble the actual parts on it.
I also don’t like using parts from unknown web suppliers just because they are cheap. I look for suppliers who were in business BEFORE there even was a web.
