I had the same question about the Brasslite 550 shown on Brasslite's website last spring fitting a caldera cone.
In particular, I was wondering why the mug then shown on Brasslite's website was called a "550" but looked exactly like (same dimensions, too) a mug called a "600" that I had purchased from Brasslite when I purchased it in 2007.
First (in April 2008), I emailed Rand at Trail Designs to learn whether a Brasslite "600" would fit the caldera cone designed for a "550" Brasslite mug. Rand sent this reply:
"Re: Brasslite 600. Here is the short story on that. BPL, Brasslite, and Ti-Goat are all ordering the same pot from the same company (King Sound) out of China. BPL's 500, 500SUL, 550, 500SUL….and Brasslite's 600….and Ti-Goat's 550ml pot…..are for all intents and purposes…the exact same thing. For sure they share the same diameter and same lid. The only difference is that BPL lengthened the height just a bit when they went from the 500 line to the 550…..and the Brasslite and Ti-Goat have a slightly different handle placement. Other than that, same pot. So much so, we "neutralized" our cone so that it now fits all the pots. You will still see some differentiation on our website as we work through old "pot-specific" inventory…..but in the future….one cone will fit all those pots. So, if we make you a Ti-Tri, and you lose the pot, you should be able to replace it through any of those sources. Now, with that said, Brasslite calling their pot a 550 now is news. However, I highly suspect, that King Sound didn't remake their titanium dies to alter the mug 1/4" in diameter just for Brasslite. Would bet money it is still the same."
Later (in May 2008), I sent an email to Aaron at Brasslite with the following inquiry:
"About a year ago (May 27, 2007), I purchased a “Brasslite 600ml Titanium Mug” from the Brasslite Website. Is that mug actually identical in all respects (height, diameter, weight, volume) to the “Brasslite 550ml Titanium Mug” that’s now listed on your website, notwithstanding the variance of “600ml” vs “550ml” in the name?
"I ask this question because I purchased my Brasslite 600ml mug to use with a caldera cone that’s described as for use with the “600ml” Brasslite mug. I have not yet purchased the cone, and the different name (“550ml”) for the mug at your website causes me to wonder whether the mug has changed in name and/or size."
I received the following reply from Brasslite regarding my question about the "550" and "600" mugs sold by Brasslite:
"No, the size has not changed. What changed was the accuracy of the volume as measured by me vs. what was reported by the manufacturer in China. They were originally marketing it as a 600 ml mug which I passed only on faith. Oddly enough, after my reporting that its volume was in fact 550, they actually changed the name on their own stock as marketed to everyone. I will send an email to Rand at Trail Designs asking him to change his name as well. Thanks for the heads up."
The above replies from Brasslite and Trail Designs would seem to answer your question, but you would probably best verify that the information provided to me still applies to the current Brasslite "550" mug.
JRS
PS — I just checked the Trail Designs website and see that it still refers to a caldera designed for a "600" mug from Brasslite:
http://traildesigns.com/products01.html#caldera
As you see from the above email from Brasslite, although the "600" nomenclature was used by Brasslite at the time that I purchased the mug, it was later renamed to "550" by Brasslite and Trail Designs says — whatever the name, 550 or 600 — the "600" caldera should fit the Brasslite mug.
Would still be a good to check with Trail Designs and maybe Brasslite, too, to be certain that your "Brasslite 550" mug will fit the Trail Designs' caldera that's described to be for a "Brasslite 600" mug before ordering.