RobiNew
You have been asking a lot of questions on this site with a strong flavour of bad formatting practices. Can I ask why you go to so much effort to avoid standardizing the document through applying styles and removing local formatting wherever possible?

In the case of this particular question, why haven't you used vba to examine a range and see what Word returns if the range has mixed font sizes. You will get the same value which translates as Undefined each time your range has mixed sizes. You can then use that value or the constant that is built in for this purpose wdUndefined.

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Andrew Lockton
Chrysalis Design, Melbourne Australia