This should help get you started. I don't think you can get 5mm as you must leave space for text at 1 point.
Sub cols()
Dim icol As Long
Dim iRow As Long
Dim otbl As Table
Dim lngW As Long
'make sure a table is selected
Set otbl = ActiveWindow.Selection.ShapeRange(1).Table
lngW = otbl.Columns(1).Width
For icol = otbl.Columns.Count To 2 Step -1
otbl.Columns.Add (icol)
For iRow = 1 To otbl.Rows.Count
otbl.Cell(iRow, icol).Shape.TextFrame2.MarginLeft = 0
otbl.Cell(iRow, icol).Shape.TextFrame2.MarginRight = 0
otbl.Cell(iRow, icol).Shape.TextFrame2.TextRange.Font.Size = 1
Next iRow
Next
For icol = 2 To otbl.Columns.Count - 1 Step 2
otbl.Columns(icol).Width = 1
Next icol
For icol = 1 To otbl.Columns.Count Step 2
otbl.Columns(icol).Width = lngW
Next icol
End Sub