Thanks.
I've found some more info as well. In summary:
HRC and HBC seem to be synonyms. Not sure where HRC originates from, though.
"High/enhanced/low breaking capacity" is well-defined, for example in
IEC 60127-2. Low is the greater of 35A or 10 times rated current. Enhanced is 150A, High is 1500A. There are other specs, like maximum power dissipation, max voltage drop, pre-arcing times per a few given multiples of the rated current. (Oddly: for slow/time-lag fuses, while "High" has generally longer pre-arcing times than "Low", at 10 times the rated current it's shorter.) UL and the likes may have additional stipulations.
I wouldn't say that's definitive, but
this random 1 page document from Littlefuse, titled "5x20mm fuse marking according to IEC 127", supports the notion that HBC = ceramic, LBC = glass:
Breaking Capacity:
L = Low (glass)
H = High (ceramic)
E = Enhanced (glass)
Speed grades (FF, F, M, T, TT) are defined as well, somewhere in
IEC 60127. At least Fast (F) and Time-delay/slow (T) are mentioned in IEC 60127-2. At least FF/F/T/TT are probably mentioned in 60127-4 (
page 12 here implies this).
BTW, I hate this practice of standards bodies/organizations to hide the specs and require payment to access them.