Forever Stems are created as a direct replacement for Missouri Meerschaum cob pipes, so those are the standards and sizes they refer to.
You are going to be hard pressed to find a replacement for a briar pipe unless it's a production run of something like a military mount where the shank and the stem do not meet flush with the same diameter, and even then it's going to be a special request to the company in most cases. Most pipes are never carved completely round and true, and this will be evident if you rotate the stem 180 degrees. Chances are when you do that you will no longer see a smooth flush joint.
If the pipe has sentimental value, your best bet would be approaching a budding new pipe maker to create something custom for you at a cheap rate just for the experience. (and understand, it might not work out) Any of the pros will likely charge you more than what a brand new Sav, Nord, or Petey would cost you.
If there's no sentimental value, then like others said above, chuck it. Buy a Dr. G. or a few cobs.
Also, to be honest, I find the price a bit steep, considering the cheapish nature of the pipe itself.
Back to the Forever Stems. Like I said earlier, they are made for cobs. A $24 stem on an $8 pipe! How's that for "steep, considering the cheapish nature of the pipe"?!
Don't be fooled, though. I own two. I don't regret the purchase, and will likely add a few more down the road. They completely change the corn cob pipe smoking experience, plus, when you burn out a cob you just move the stem to a new one. Consider it a lifetime investment!
