I've never seen DI fuses in real life... and DIV only once.
A big municipial apartment building had D IV 80A fuses for the main feeder. Nowadays only a system called NH is used for such big fuses.
D IV isn't sold in Austria any more, which leads to interesting occurences...
Around christmas (I think actually on 24th or 25th) a guy from the company where I had my summer job got called to a big apartment building at 7 am. No power in the entire house. First guess has to be something with the riser, otherwise at least parts of the house would have power. Opens the box... all three riser fuses along with the screw caps had been stolen during the night! Were lucky the pulled them during a low-load period... unscrewing such a beast under load must give a nice bang and fireworks!
Good screw caps have a spring inside that hold the fuse quite nicely. If that spring weakens I dump the screw cap. Good hardware stores still sell new DII and DIII screw caps, key rings and fuses, but the screw caps just look new, so I usually try to scrounge up old ones. That's not too hard, especially working for an electrician I could get several per day since we were ripping them out basically everywhere. During the four weeks I spent there I took out three complete Diazed panels.
Historically Austria never separated lights and sockets. There was one or more DII circuits for everything, depending on the size of the house/apartment. Before WWII usually 4A, later 6A, from the 1960ies onwards general purpose circuits were usually 10A. 16A was occasionally used for dedicated circuits, but mostly for deliberate overfusing. 20A and 25A are typical sizes for feeder fuses (1x 20 or 25A serves apartments up to 100 square meters quite nicely, 3x25A are usually enough for an older single family home. 35A and up are mostly used for big old single family homes and as riser fuses in multi-family buildings.