AutoFit.bas

Type StoreRangeInfo
    'TODO: Store workbook name, file name.
    Columns() As Variant
    Widths() As Variant
End Type

Public AutoFitUndoData As StoreRangeInfo

Private Sub PrepareAutoFitUndo(Rng As Range)
    ReDim AutoFitUndoData.Columns(1 To Rng.Columns.Count)
    ReDim AutoFitUndoData.Widths(1 To Rng.Columns.Count)
    Dim x As Long
    x = 1
    For x = 1 To Rng.Columns.Count
        AutoFitUndoData.Columns(x) = Rng.Columns(x).Column
        AutoFitUndoData.Widths(x) = Rng.Columns(x).ColumnWidth
    Next
End Sub
    
Sub AutoFit()
    If TypeName(Selection) <> "Range" Then Exit Sub
    
    Dim SU As Boolean
    Dim Sht As Worksheet
    Set Sht = ActiveSheet
      
    With Application
        Call PrepareAutoFitUndo(Selection)
        SU = .ScreenUpdating
        .ScreenUpdating = False
    
        With Selection
            .EntireColumn.AutoFit
        End With
        
        If Selection.Columns.Count > 1 Then
                Dim x As Long, max As Long
                
                For x = 1 To Selection.Columns.Count
                    If Selection.Columns(x).ColumnWidth > max Then _
                        max = Selection.Columns(x).ColumnWidth
                Next
                
                Dim r As Range
                For x = 1 To Selection.Columns.Count
                    Set r = Selection.Columns(x)
                    r.ColumnWidth = max
                Next
                
                Application.ScreenUpdating = SU
        End If
    End With
    
    Application.OnUndo "Undo the AutoFit macro", "AutoFitUndo"
    
End Sub