If you like to swap out your favorite briar's 9mm filters particularly often, to keep the cleanest, smoothest smoke, you may want to get your Dr. Perl Junior filters in numbers a bit more substantial than the standard 10 pack. That being the case, you'll love this item: The genuine Dr Perl charcoal filter, in a 40-count box.
I don't always smoke filter pipes, but when I do I prefer this filter (read it with an aristocratic Spanish Accent :). Good value, large volume and effective in all the 9mm filter pipes I own. -Best Regards, Dave Ray