This tip comes from Northeast Alpine Start.
The “quad” anchor, first mentioned around 2006 by John Long in his book “Climbing Anchors”, was an attempt to have the Holy Grail in anchors - good equalization, minimal extension, quick to set up, and super strong. Plus, it had the bonus of two independent and equalized master points, which can be quite handy. Well, it never quite caught on, for a variety of reasons, one of which the original version suggested using a long and bulky cordelette to rig it.
Traditional “quad” anchor rigged with 7mm cordelette. Nothing really wrong with it, just big and bulky.
Well, here’s the next iteration of that idea, in a much lighter and more compact package. Call it the mini quad. Rather than using a huge honker cordelette, instead you use a double length / 120 cm (or better yet, a 180 cm runner, more on that below) sling, double it, tie overhand knots as close to the ends as possible (with the stitching in one of the end loops), and then use either three strands (toproping) or two strands (multipitch) in the standard quad set up.
The knots stay in the runner for at least the entire day. AMGA Guide Dale Remsberg uses this system a lot, and told me he likes to untie the knots every few days or after a weekend of climbing. In the article linked above from Northeast Alpine Start, Dave said he prefers to keep the knots tied pretty much permanently in the runner, and then retire the runner every year or so.
This system works best with two solid pieces of gear that are fairly close together and ideally in a horizontal plane. Two bolts on a sport route are a perfect application. Two ice screws that are slightly offset would also work too. (If you’re building in anchor from trad gear, it's probably going to be faster and more efficient to use a more traditional cordelette.)
Have a look at the video below and this link for more ideas how to do this.
120 cm Dyneema runner tied as a mini quad with two bolts.
In action, it can look like this. The leader is cloved to the yellow carabiner (on right) and can belay the second from a Munter hitch or a plaquette style belay device, shown here on left.
One additional benefit of this system is that it gives you a ready-made rappel extension sling. Here's how that works (video screen grab).
Plus, it’s light, compact and easy to rack.
Now, for those of you who have a freak-out about tying a knot in Dyneema, this system may not be for you. A full strength Dyneema runner is about 22 kN, tying a knot in it might reduce that by about half, so you're still around 10+ kN, which is more than enough to hold pretty much any conceivable force in a climbing fall.
You have to use skinny Dyneema for this. (It will not work with a nylon runner because the knots are too big.)
You need to tie the loops carefully and make the knots not much bigger than a coin - just big enough for a carabiner to fit through, and not much bigger.
It’s best practice to untie these knots knots several days of climbing and retie them in a different spot, to spread out any load from any one place.
Keep in mind that a 4 foot/double/120 cm runner is JUST barely long enough to do this. For many applications, a 180 cm sling may be better. Try this first with a 120 cm runner. If you think you want a little more length, get a 180 cm runner, although it can be a bit hard to find. (Some folks favor a 240 cm runner, but I found that to be too long.) Petzl and Mammut make a 180 cm runner, which for me is kind of a sweet spot in terms of length. I'm sure you have a double sling already, so start with that and see if it works for you before you special order a longer one. (If the links below don't work, just Google around until you find them.)
Here’s a comparison of the Petzl Pur’Anneau 180 cm sling on the left and a standard 120 cm double sling on the right. You can see the 180 cm sling gives you quite a bit more length to work with, which is handy if the gear is farther apart or offset.
And here’s a nice video showing how it works.