Bowers & Wilkins Nautilus 804 Midrange speaker removal


First time posting here. 

Does anyone know the tool needed to unscrew  the drawbar holding the midrange speaker on Bowers & Wilkins Nautilus 804. I have tried a 6mm and 1/4 inch deep sockets and none of them work. I also cannot find any information online. Any leads are appreciated. Thanks

fabkith