I first heard of this technique from IFMGA guide and technical director of the American Mountain Guide Association (AMGA) Dale Remsberg, and a video made by the German Mountain and Ski Guides Association (VDBS).
Links to source material below.
If you try to tie a cordelette style anchor with an overhand knot in a double length / 120 cm runner clipped to three pieces of gear, the knot takes up so much material that it fails. Given this, for a three-piece anchor, most climbers would automatically reach for their cordelette.
But, there’s another option. Provided the gear is close together, the 120 cm runner works great if you make a girth hitch at the master point rather than an overhand knot.
The same technique also works with a two piece anchor and a single length / 60 cm runner:
Now, most of the time, for a two piece anchor, provided you have a double length/120 cm runner, tying off in the normal overhand knot is still a perfectly fine technique. But, if you get to a two piece anchor and find you only have a single length / 60 cm runner left, or you don't want to deal with untying a welded knot, or if you think caring a huge cordelette is kind of a PITA, this is an solid alternative.
A previous tip covers using a clove hitch at the master point, a closely related technique.
And of course, you can use just the rope to make an anchor: A slick way to build an anchor from the rope and Use the rope to connect to your anchor - 2 knots to know
Why might you want to have a girth hitch at the master point?
Easy to untie after it’s been loaded (no welded knot to deal with)
Easier to untie if hands are sore and/or cold, or you’re wearing gloves
Keeps the master point carabiner properly oriented, it can never spin and become cross loaded
You can equalize three placements with a 120 cm runner and two placements with a 60 cm runner, if the bolts/gear are close together
Redundant (even though it may not appear so at first glance. Really it is; cut one strand and it still holds.)
Plenty strong (yes, anchor engi-nerds, girth hitching weakens a sling a bit, but this is a 22Kn runner; are you really worried about it?)
I’m not suggesting that everyone always use this as standard procedure. This technique is meant to show more advanced climbers another tool in the toolbox, not as a perfect technique for every situation.
Hey, don’t listen just to me. How about these reputable endorsements for the girth hitch master point?
Ortovox (a German company best known for avalanche transceivers and related ski mountaineering gear) has an excellent Youtube tutorial video series on many aspects of mountaineering. The video series has the (somewhat awkward) title of “Safety Academy Lab Rock”. It's produced in partnership with Petzl and the German Mountain and Ski Guides Association (in German, “VDBS”). So, you can probably assume that the techniques shown have technical approval at the highest levels.
The video below shows various guides building multi piece anchors using an open (aka untied) cordelette.
In every case, they use a girth hitch to create the master point.
(The climber in the video is also using two techniques uncommon in the United States: 1) using an overhand knot to make a loop from his cordelette; and 2) threading the open/untied cordelette directly to the pitons / protection without using carabiners.)
Watch the video below. (The whole video is only 3:30, but if you have a short attention span, start at 1:00 and 2:00. )
Note the girth hitch at the master point in the thumbnail image below (and yes Eagle-Eye, this is for a four piece anchor.)
Dale Remsberg is an internationally licensed mountain guide (IFMGA) and technical director of the American Mountain Guides Association (AMGA). He has a great Facebook feed with regular tech tips. On it, he recently highlighted the girth hitch as a master point, calling it one of his “go to’” anchors.
Below is a screen grab of his post.
The photo and comments from Dale’s post:
I get it that everyone is not going to be thrilled with this as an anchor technique. And that's OK, you don't have to.
In the end, everyone has personal accountability for their own choice of technique and level of perceived safety. (That's why they call it the “Freedom of the Hills”, right?) But, at least be open to new ideas, especially if they come from reputable sources.