This is the buckle found on the front chest of the Personal Restraint System, the one that secures the arm loops to the harness.

This one is pretty simple, I didn't add anything like a detent or button because that would make it too bulky. I don't want two big metal boxes on the chest of my straitjacket anymore!

So yeah. This one screws together with the same hex tool as type 1. Again, this is a simplified render of the buckle. The actual product will have rounded corners and beveled edges.

Since there are no additional diagrams for this one, I also did two renders of the final, beveled buckle attached to straps. Can be found in scraps here:
https://www.furaffinity.net/view/36201408/

Full size version and additional renders available to all patrons on Patreon here:
https://www.patreon.com/posts/36411634