For years, ice climbers, mountaineers, and skiers have drilled side-by-side holes into ice, and slung the connected horizontal “V” as a V-thread anchor. But there’s a better option for nearly every situation. IFMGA certified ski and mountain guide Howie Schwartz, owner of Sierra Mountain Guides, gives us the story.
I cannot say that I am an expert on that topic and would welcome a discussion on the speculated pros and cons of these different techniques. As I understand them, they are almost identically the same and for the same applications with the only difference being the orientation, and that the vertically oriented “Anderson thread,” or “A-thread” as it has been called, has tested in limited studies as notably stronger. The orientation of the holes may be a consideration with regard to the shape and topography of the ice in the location of the anchor. In flat, homogenous ice I am not aware of any circumstances where a traditional V-thread would be advisable over an “A-thread.” The vertical orientation may be more difficult in some circumstances to place as water ice tends to form in the vertical plane and may make it harder to incorporate the maximum amount of ice between the holes, which appears from studies to be a more critical factor than orientation in maximizing anchor strength in solid, well-attached ice.
Howie’s views are supported by testing done by multiple parties, including Seattle Mountain Rescue and fellow guides Vince Anderson and Mark Beverly. Their findings determined that horizontal ice threads are weaker (from 12%-27%) and have no benefit unless you’re in an extremely rare situation where solid ice only exists in a small horizontally-dispersed area. Howie continues:
I see the (vertical) “A-thread” as a small evolution and improvement in the technique of placing V-threads, not as a visionary and distinct technique that warrants a new name. Diagonal V-threads appear to be untested. If they prove stronger will we call them “D-threads?” Suffice it to say, we discover new things about the physics of climbing as people continue to use and test climbing tools and techniques. We hope these discoveries will ultimately increase the safety of our pursuits.
Since ice typically fractures across a horizontal plane, the vertical “A” thread anchor will also be less prone to catastrophic failure. And a final benefit to the vertical design is that gravity makes it much easier to feed webbing or cord through the ice from the top hole in the “A” design. In smooth and completely frozen (no surface water) ice, a bomber anchor can even be made without using any cord and not leaving behind garbage if you simply thread your rope itself down through the ice. Just remember to tie any knot between ropes below the bottom ice screw hole, so you can pull your ropes straight down, not up and through the thread you’ve drilled.