I hope this isn't too simple-minded to mention, but it appears that the Savenelli adaptor that eliminates the balsa wood filter but also narrows the airway so it isn't wide open also works nicely in other pipes that accept a 6mm filter like the Dr. Grabow Royalton bulldog, in my case, or probably in filtered MM cobs. 'Realize this hardly makes me Thomas Edison, but it is useful for those of us who love our Dr. Grabows but really don't want to smoke them with a filter or with a wide open draw. I'm field testing it now with the Royaton bulldog and will report back after a bowl or three. Seems to work fine. The Savenelli adaptors are available at most retailers; smokingpipes.com carries a package of five for four bucks. It's like wheels on luggage; why didn't I think of this long ago?