Hi Mark,
The only in-built fractions in every font are ¼, ½ & ¾. Some fonts have support for thirds and eighths also, but anything else you have to create for yourself. And, whereas the in-built fractions consist of a single character, your own will consist of three or more characters. The following macro will convert your own fractions to an approximate visual representation of the in-built fraction characters. If you use it, I'd suggest not using the in-built fractions, so that the appearance is consistent throughout the document.
Code:
Sub Fraction()
Dim RngTmp As Range, StrFrac
With Selection
StrFrac = Split(Selection.Text, "/")
Set RngTmp = .Range
With RngTmp
.Font.Size = .Font.Size * 0.875
.End = .Start + Len(StrFrac(0))
.Font.Superscript = True
.Characters.Last.Next.Font.Italic = True
.End = .End + 2 + Len(StrFrac(1))
.Start = .End - Len(StrFrac(1)) - 1
.Font.Subscript = True
End With
End With
Set RngTmp = Nothing
End Sub