Double D-ring buckle for 20mm strap webbing

Application

The double D-ring buckle for strap webbing is not the fastest to close, or the easiest to open. But it is the strongest there is to my knowledge (see video at the bottom of this page).

If you need a quicker or more convenient buckle with moderate strength, please check out my other publication: https://www.printables.com/model/415338-snap-fix-for-strap-webbing-20mm-and-25mm-versions

If you came here looking for a double D-ring buckle for the more commonly used 25mm straps, you will find a fitting design here, which is online for quite a while already: https://www.printables.com/model/121235-double-d-ring-buckle

Printing

This part is very simple to print. Just print it in the uploaded orientation with a lot of perimeters (4-5) and 100% infill for optimal strength. I typically use PETG for functional parts, but I would strongly assume that PLA works as well. Just keep in mind that PLA will “flow” over a longer time when it is under constant load. So you buckle might come loose over time.

Assembly

You need to form a closed loop with the strap that is attached permanently to the two ring rings. You can either do this with the strap tensioner shown in the photos. I have added a 20mm version to this publication for your convenience. 

If you need a 25mm strap tensioner, it is already available here: https://www.printables.com/model/121221-strap-tensioner-load-optimized

Another way of forming the closed loop is by simply gluing it with super glue (cyanoacrylate), which gives very strong loop if you use clamps and give it enough time to cure. I cannot stress enough how import the clamps are. If you simply press it together with your fingers you will not reach the same pressing force and you will likely not have the patience to hold it long enough. If you have no well suited clamps, feel free to get yours here: https://www.printables.com/model/84103-one-inch-clamp-25mm-opening

Usage

The rule to use double D-rings is very simple:

Go in through both rings and back through one ring. 

A more graphical description can be found in the video that I linked to below.

Disclaimer

Although this kind of buckle was load-tested by me to several tens of Kilograms, they will finally break under high load if you stress them a lot. For all my applications this was by far good enough, but you mileage may vary. Use at your own risk.

Video on load testing and usage of double D-rings