dan', this is the very opposite of a dumb question. This is a question every new pipe smoker should ask but usually doesn't, and has to learn the hard way buy buying various pipes and having questions and uncertainties. Some of the more common filters are 6 mm filters --including Dr. Grabow, Medico, and Savenelli balsa and Savenelli adaptors that allow you to smoke without a filter but still maintain an airway the same size all the way through. Most pipes that use filters can be smoked without the filters, but this opens the airway quite a bit -- some find this a little too open and airy, and others like it fine. The stingers mentioned by darwin aren't used in most new pipes today, but you do need to check when you buy pipes. Some can be slipped out with no problem. I don't believe new Dr. Grabow pipes have these, nor do Kaywoodies of recent manufature, although you might find them in "new" pipes in an old inventory. There's more to learn and know about filters, but that gives you a groundwork. Not a dumb question to ask, but a really, really dumb question not to ask. Other common filters are 9 mm, and there are adapters available for those, and Brigham rock maple inserts, not really filters but more like wood tube airways, which I think are optional to use or not. Incidentally, the Savenelli adapters can be used in any 6 mm filter pipe, like Dr. Grabow, Medico, and Yello-Bole. One other point -- Savenelli makes most of its pipes to accept the 6 mm balsa filters, or adapters for no-filter smoking, but they also have several lines, such as Oscar Lucite, their churchwarden 601, and unfinished pipes, among others, that do not have filters at all.
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