Is the 3mm/4.9mm the diameter of the shaft that the tips fit over?
I've tried various lookups of my JVC HA-FX40 buds, but they're not consistent with the HA-FX45S (which are on Dekoni's table).
1234567890Okay, will answer my own question since I'm a bad-ass and I have a metric ruler and research skillz.
The 3mm/4.9mm measurement is going to be the diameter of the shaft on your buds. If you're duckduckgoing for specs, then include the term "bore" (i.e., shaft diameter) in your search phrase, and it might help.
Although I doubt anyone else around here cares about a low-end set like the HA-FX40, I can confirm that the bore of these is just a hair under 5mm, so you'd want the 4.9mm tips.