What about 7 mm Metric Hex? I notice a lot of Metric Hex kits skip 7mm, but my Craftsman set has the 7 mm Hex Socket. My fold up Hex Keys all skip 7 mm and 9 mm.
Metric Hex sets tend to skip 7, 9, 11, 13, 15, and 16 mm.
Most of the Metric Hex sets I'm seeing go from 1.5, 2, 2.5, 3, 4, 5, 6, 8, 10, 12, 14, and 17mm. Like these:
http://www.amazon.com/dp/B0007GGUBU/?tag=atomicindus08-20
But then SK offeres this set that doesn't skip any sizes:
http://www.amazon.com/dp/B0002NYC2W/?tag=atomicindus08-20
I guess a lot of people here wouldn't skip any sizes, but it gets a little crazy. I have never needed a 7mm hex, but use 6 and 8 all the time. Same with 9 mm. I wonder who comes up with these sets and decides which numbers to skip? They all seem to follow some sort of path, because different tool companies all tend to skip the same basic sizes. They may be on to something.
Who comes up with these sets? Does someone have a career in "tool set design", and he's an expert on which sizes are hardly ever used? Can I trust these people?