History

This part is actually a redesign of a surplus part to my magic strap buckle:
https://www.prusaprinters.org/prints/84848-magic-strap-buckle-magnetic

I got some feedback from a user that was very happy with the buckle, but had somehow managed to break the added strap tensioner. That got me started on doing load tests on different straps, buckles and tensioners. I actually never managed to break a part with the 120 kg of load that I can sensibly produce. But in some situations, which were actually not part of the correct usage, the strap managed to slip somewhat under high loads. This part is now the final development result that addresses all issues that I could reproduce during my tests. 

There are intentionally no chamfers on edges that are meant to bite into the strap and prevent it from slipping.

Different sizes

All the load testing has been done on the 25mm (one inch) wide part. But for those of you that like the 20mm wide straps (like I do), I have also uploaded a 20mm version, which was actually part of another publication from me already. 

Usage instructions for best load carrying capabilities

The correct (and most load resistant) usage for this part is as shown in the pictures. The strap comes from one side, goes through the tensioner (in and out on the bottom side, passing over the middle). Then the strap does a loop, typically through a buckle, but can also go around a pole or any other object. The strap comes back from the object and goes again through the tensioner, this time on top of the other strap. 

It is of importance that the returning strap layer is on the top side, if you want to achieve ultimate strength. The lower layer is somewhat more prone to slipping, but will not slip if there is force from both sides (the strap load from the side and opposing force from the loop). 

Printing instructions

Printing this part is very simple. No supports or brim is needed. Simply print the part laying flat on the bed, with 100% infill for maximum strength. In my tests both PLA and PETG have survived all load tests up to 120kg (1200N) without any visible damage.

Disclaimer

Please don't be a fool and risk any loss to property or even injury or death by using this part in mission critical applications. Use it completely at your own risk.