There are two models, one with teeth and one without. I recommend the model with teeth. This will prevent slippage of the straps.
Update 28SEP2018: I uploaded a strap keeper to hold the straps together.
Although it looks very similar to the original model, this is a complete redesign. I made some changes that suited me better. It has less play and self-centers when clicking the parts together. I also made the button smaller, although it's just as easy to use.
The buckle is self-tightening. The harder you pull it apart, the more engaged the locking mechanism becomes. Under load, it will not slip apart unless it catastrophically fails.The engagement has a very satisfying click when you connect the two parts together.
You could also use this as a belt buckle.
I have uploaded two models for each part. The only difference is the strap hole sizes. Most people will probably use the large size.
I printed these at 80% scale which produce a strap hole width of 21mm.
Native size produces a strap hole width of 27mm.
Please post your makes and comments!
Check out my other designs https://www.thingiverse.com/mistertech/designs
30% (probably doesn't matter)
At 80% scale, it took 41 minutes to print a set.