This is a belt that worked for me for a long time now. The buckle has changed over time, but the belt part of it works fine.

Things to note,

1. The buckle needs to be printed out of TPU. Personally I would recommend not having the printer to cross walls to help with stringing. But some might be able to print as is with no problem. Remember TPU shouldn't go through the AMS.
2. The buckle has changed over time. The first one (v2 flag) is the newest version. This one removes the need for the rod and it replaces it with a screw. The point of this is the screw (or in this case 2 screws adds strength to the buckle that I couldn't get otherwise. And the amount of metal is so little that metal detectors at airports don't go off (or maybe it is because I'm using stainless-steel ones). When I get time I will upload a blank.
3. You can use most any design on the buckle. Take a bank buckle, put it in 3D builder on windows. Take the design you want. Place it, subtract it, and now you have the design you want. Note the support blockers.

You can print the buckles out of PETG. I just have PLA on hand so I used that.