constructor TTestComp.Create(AOwner: TComponent);
begin
  inherited;

  // ...

  // Thread-Instanz
  FCon2SvrThd := Nil;
end;

destructor TTestComp.Destroy;
begin
  // cleanup everything
  // ...

  // End Thread if running
  if FCon2SvrThd <> Nil then begin
    FCon2SvrThd.Terminate;
    While FCon2SvrThd <> Nil do begin
      sleep(250);
    end;
  end;
end;

procedure TTestComp.OnConnection2SvrThreadEnded(Sender: TObject);
begin
  FCon2SvrThd := Nil;
end;

procedure TTestComp.StartThread;
begin
  FCon2SvrThd := TTwConnection2SvrThread.Create(self,FTcpCon);
  FCon2SvrThd.OnThreadEnd := OnConnection2SvrThreadEnded;
  FCon2SvrThd.Resume;
end;

constructor TTwConnection2SvrThread.Create(ParentComp : TTestComp; TcpCon: TIdTcpClient);
begin
  inherited Create(true);
  FreeOnTerminate := true;
  OnTerminate := CleanUp;
  fParent := ParentComp;
  fTcpCon := TcpCon;
  fSendCS := TCriticalSection.Create;
  FOnThreadEnd := Nil;
end;

procedure TTwConnection2SvrThread.Cleanup(Sender: TObject);
begin
  Disconnect;
  FreeAndNil(fSendCS);
  if Assigned(FOnThreadEnd) then
    Synchronize(syncOnEnded);
end;

procedure TTwConnection2SvrThread.syncOnEnded;
begin
  FOnThreadEnd(self);
end;

procedure TTwConnection2SvrThread.Execute;
begin
  While (not Terminated) and (fTcpCon.Connected) do begin
    // do some work ...
  end;
end;

function TTwConnection2SvrThread.Disconnect: Boolean;
begin
  if fTcpCon.Connected then begin
    try
      // Send Logout Command
      fTcpCon.WriteLn('QUIT');
      fTcpCon.Disconnect;
    except {} end;
  end;
  result := not fTcpCon.Connected;
end;