const
  TBM_GETTHUMBRECT_2 = WM_USER + 45;
  TBM_SETTHUMBRECT_2 = WM_USER + 48;

  TTrackBar2 = class(TTrackBar)
  private
    FThumbRect2: TRect;
    procedure SetThumbRect2(var Message: TMessage); message TBM_SETTHUMBRECT_2;
    procedure GetThumbRect2(var Message: TMessage); message TBM_GETTHUMBRECT_2;
  end;

procedure TTrackBar2.SetThumbRect2(var Message: TMessage);
begin
  FThumbRect2:=PRect(Message.LParam)^;
end;

procedure TTrackBar2.GetThumbRect2(var Message: TMessage);
begin
  Message.LParam:=IntPtr(@FThumbRect2);
end;

var
  R, R2: TRect;
begin
  SendMessage(Handle, TBM_GETTHUMBRECT_2, 0, IntPtr(@R2));
end;