Sub ChangeSizes()

    For i = 2 To 50
        Range("G" & i) = LookupSize(Range("G" & i).value)
    Next i

End Sub

Public Function LookupSize(Size) As String

    Select Case Size
        Case Is = 1
            Return '5/8" or 1/4"'
        Case Is = 43
            Return '3/8"'
    End Select

End Function

Public Function LookupSize(Size) As String

    Select Case Size
        Case 1
            LookupSize = "5/8" or 1/4"
        Case 43
            LookupSize = "3/8"
    End Select

End Function

Public Function LookupSize(Size) As String

Select Case Size
    Case 1
        LookupSize = '5/8" or 1/4"' or whatever you want
    Case 43
        LookupSize = '3/8"' or whatever you want
End Select

End Function