Thread

type
   TMyThread = class(TThread)
   private
      fLowerLimit: Integer;
      fUpperLimit: Integer;
      procedure UpdateMainThread;
   protected
      procedure Execute; override;
   public
      constructor Create(lValue, uValue: Integer; Suspended: Boolean);
   end;

implementation

  uses MainForm; //Unit of the form that will be updated by thread

constructor TMyThread.Create(lValue, uValue: Integer; Suspended: Boolean);
begin
   Inherited Create(Suspended);
   fLowerLimit := lValue;
   fUpperLimint := uValue;
   FreeOnTerminate := True;
end;

procedure TMyThread.Execute;
var
   I: Integer;
begin
   For I := fLowerLimit to fUpperLimit do
      if (I mod 10) = 0 then
         Synchronize(UpdateMainThread);
end;

procedure TMyThread.UpdateMainThread;
begin
   MainForm.Memo1.Lines.Add('Hello World');
end;

end.