This is a spacious case designed for the Raspberry Pi Zero and Zero W. Especially useful is the external SMA antenna mount. I have modified my rpi0w to use an external antenna by soldering a U.FL connector to the provided pads next to the micro USB port. You must also reposition the 0 ohm resistor to disconnect the onboard wifi antenna and route the signal to the external connector. This can be done by rotating the SUPER TINY resistor toward the provided soldering pad. I used a hot air soldering iron and solder paste with flux, and a very fine strand of wire to carefully nudge the resistor.
You could also use the SMA mount to connect small RTL-SDR and hide it in the case.
The case was designed to use M3 hardware. The bolts are M3 16mm.
You may need to use a 1/8 in drill to clean out the holes. I also had to run the 1/8" drill through the raspberry pi mounting holes to make room for the M3 hardware. But as you can see, everything fit perfectly. It, may also be possible to keep the top on using friction as it is a tight fit.
There is enough room inside for a small battery or whatever else project you can think of.
Amazon Basics PETG