If you've purchased a MM cob recently you may have noticed that the bit (as they call them) was loose.
Recently made MM pipes with the loose bits and ferrules have a wooden stem that MM is getting from a new vendor in Maine. Since they have about 150,000 of the new wood stems in stock they have attempted to come up with a way at the factory to “swell them up”. As experienced cob smokers know, the wood stem swells up some after they are smoked, so normally within a few smokes they fit snugly.
1.) Smoke it. As I said above, this usually does the trick after just a few bowls.
2.) If the bit is too loose to even get a few bowls smoked I wrap a single wrap of Teflon tape around the tenon. Since the stem will swell quickly enough I now use this option instead of modifying the stem or tenon and once things tighten-up I remove the tape. No Teflon tape on hand? Use any tape you have on hand but understand that you'll have to use a solvent to remove the sticky adhesive residue.
3.) Use the "hot water method" to heat the tenon and once soft gently press the end of a pen into the tenon to cause it to swell slightly. I no longer use this method as my first line of defense because once the wooden stem swells the bit will be crazy-tight.
4.) Glue a strip of paper or a shaving from a hand plane inside the stem. I even did a video on this several years ago.
I haven't done #4 in years, but if 1-3 don't work this is what I've done in the past. If you purchased your pipe from us and it doesn't tighten-up, we'll replace the pipe.
Here are a couple old vids on the topic: