This image from my book ‘Down’ gives a rough guide to snow/ice bollard sizes, ranging from small (hard snow) to large (soft snow). There should probably be a micro one for pure ice, which can be fist size, and a massive fuck-off one, for the powderish powder. The bollard is something that most winter climbers will build once, generally on some winter freshers course, along with ice axe arresting, maybe digging a snow pit, and then forget about. This means that when the day comes when you either need to use a bollard as an anchor (belay or rap), you’ll have all the experience and knowledge as a sport climber would building a 10 point equalised belay in disintegrating limestone. Whenever you have time, say at the end of a short day climbing, or when the weather is crap, you should always try and polish your skills.
This can be fun stuff like going out and digging some snow shelters (snow pit, covered and uncovered, snow holes, Quinzee, igloo), or even just bivvy out on a local crag in winter conditions to learn how it’s done. Ice axe arresting is like learning how to use a reserve parachute, i.e. you need to know more than just the theory. Yes, it seems like a newbie thing to do, but climbing is full of climbers who just slipped to their deaths without even trying to stop themselves (did they not know how to do it, did they freeze, did they just hope they’d just hit a soft patch?). The trick with arresting is doing it instantly, as well as knowing how to attempt it sans axe, going backwards, upside down etc.
Remember that in the high mountains, what gets you are slips and trips. As for the bollard, just like the ice thread, it’s something you should build and then test to destruction. Build one and then try and break one, both with someone belaying from one, as well as a rap an anchor, you and your partners trying to cheese wire it through the snow, pulling together, learning to together as if your lives depended on it (because one day they may well)