Alternate clamp to mount the Nikon TC-E2 for the popular DIY stargazing binoculars that is fabricated from laser cut material, thickness of the material should be 5 mm. I am using acrylic.
The mount is clamping the teleconverters with two M3 bolts. Length of around 10 mm should fit, but there is a lot of space so you can also drill a bit deeper.

The parts have to be cut out twice, the second set mirrored (or just flipped around :))

Then glue the two different parts together, so that the gaps coincide. Use a better glue than i did and a bit of pressure, then the parts will stay transparent. For Acrylic, Acrifix 0192 should be good.

After gluing, the clamp part has to be drilled out and tapped for M3. This might be difficult to do and will require a strong glue connection. Since its plastic, i got away by filing a threading tool from an additional M3 bolt instead of buying a tap.
For M3 the pilot hole has to be 2.5 mm. For me, 2 mm worked as well with a very shallow tap. It helps to put a piece of plastic inside of the gap to guide the drill and tap.

The hinge requires a 10 mm outer diameter pipe or rod. You can glue it on one side or mushroom the ends a bit. Length either 10 mm, or 15 mm with the adapter for the head mount. You can see in my pictures, that i glued the rod into the head mount and greased it at the holes for the clamps. Without the GoPro mount you can glue it to one of the clamps.
The parts are not fixed axially. This makes it easy to take apart ant put the clamped teleconverters into their bags. Even with grease, the friction is still high enough to make this safe without it falling apart during use. I will have to check how this develops with more use.
If you do not like this, put a bolt through the rod with and fix it axially with large washers on each side.

The parts for the GoPro head mount contain longer "legs" and slits than required, so that you can fit and cut them for your own head size and eye distance. If you cut it from the same material as the rest, the les have to be ground down to a thickness of 3 mm. Don't do that if you cut them yourself.

The bino_clamp_laser_drawing_svg.dxf contains all required parts + GoPro head mounts layed out. Rename to .svg, thingiverse does seem to only allow .svg uploads for the thumbnail.