In reply to Chaildn:
The advice I had from a British Mountain Guide whom I hired for a few days alpine training (2017) was that 1x long (20cm+) and 1x medium (16-17cm) screws are good for each member of the party. This also matches recommendation in the book Alpine Mountaineering, by Bruce Goodlad (also a BMG).
Reasons given were:
1. securing yourself in and potentially aiding yourself out of a crevasse if you slot. Obviously has a few assumptions about being conscious, being able to move and reach the side, etc.
2. potentially still useful as a hauling anchor if you're not the one who slots, i.e. thin or really soft snow covering where you could potentially dig to ice, although buried axe remains the more likely option.
3. protecting steeper icy sections. There are a few routes I'm aware of in the PDish range that I've heard can get icy and steep enough to be worth protecting, e.g. crossing the Passo del Naso from Quintino Sella to Refugio Gnifetti in Monte Rosa, and SE ridge of Alphubel, where screws give you an option for at least running anchors. Obviously you'd ideally then have a corresponding number of quickdraws too in that case although could I guess jury rig some out of long slings tripled up and spare krabs.
Also the long screws give you the option of v-threads if you end up descending steeper iced slopes although again I haven't run into a need for that yet.
So I've always carried two screws, though haven't needed them in anger yet. The reasons given to me seem sound so I'll continue to carry them. In terms of what screws my view is that it probably doesn't really matter, though mine have handles on them for ease of winding them in and out.
Post edited at 04:08