Peter A Forbes said:
These were made by Belling-Lee IIRC, they called them the '00' fuse cartridge
and made one of their panel fuseholders with different caps, one for 5 X 20 and
one for this size.
I don't know of anyone making them now, but have a look at Bulgin's web site and
see if they have them listed.
Often, if you come across vintage gear with bizarre fuse sizes, it is easier
to just make some adaptors to put a modern fuse in there than it is to do
anything else. It's usually a matter of finding some brass stock that is
the diameter of the fuse you want, cutting two short pieces to length, then
drilling holes into each one whose diameters are that of the modern fuse
you wish to use. It helps to have a lathe but you can do it with a hacksaw
and a hand drill if you're careful.
--scott