次のサンプルコードは、セルの周囲の罫線を1本の線にまとめて罫線を細くします。
fpSpread1.ActiveSheet.Cells[0, 0, 30, 30].Border = new FarPoint.Win.LineBorder(Color.Red, 2);
fpSpread1.BorderCollapse = FarPoint.Win.Spread.BorderCollapse.Collapse;
FpSpread1.ActiveSheet.Cells(0, 0, 30, 30).Border = New FarPoint.Win.LineBorder(Color.Red, 2)
FpSpread1.BorderCollapse = FarPoint.Win.Spread.BorderCollapse.Collapse