The V-thread -- also known as the Abalakov anchor -- is a simple technique wherein one simply links two holes bored in the ice together and then threads a cord through, the cord is then tied-off and used as an anchor.
Following is a short video on how to do this with a single ice screw:
It's not a bad idea to back-up an ice anchor before rappelling. This article provides some tips as to how one might back-up a V-thread.
It's a good idea to practice this on the ground before employing it in a descent. Though this is conceptually simple, it can be difficult to line up the bore holes. This is definitely not something that you want to use for the first time in a raging snowstorm as it's starting to get dark.
--Jason D. Martin
