A BorderPart object represents a particular part of a border around a cell or area of cells.

 public class BorderPart
Public Class BorderPart

To get a BorderPart, use Border.Item.

          ExcelApplication xla = new ExcelApplication();
          Workbook wb = xla.Create();
          Worksheet ws = wb.Worksheets[0];
          Area a = ws.CreateArea(4, 4, 15, 6);
          Border b = a.BorderAround;
          BorderPart bp = b[Border.Part.Left];

          Dim xla As New ExcelApplication()
          Dim wb As Workbook = xla.Create()
          Dim ws As Worksheet = wb.Worksheets(0)
          Dim a As Area = ws.CreateArea(4, 4, 15, 6)
          Dim b As Border = a.BorderAround
          Dim bp As BorderPart = b.Item(Border.Part.Left)