type
  TMyThread = class(TThread) 
  private
    parent_class:pointer;
  protected
    constructor Create(suspended:boolean;parent_class:pointer);
  end;

type TMyClass = class
  private
    MyThread:TMyThread;
  protected
    MyField:TDumbField;
  end;

constructor TMyThread.Create(suspended:boolean;parent_class:pointer);
begin
inherited Create(suspended);
self.parent_class:=parent_class;
end;

procedure TMyThread.Execute;
begin
TMyClass(parent_class^).MyField:=arrgh;
end;

procedure A;
begin
MyClass:=TMyClass.Create; 
MyClass.MyThread:=TMyThread.Create(true,MyClass);
end;