Modular holder system (3rd hand / lab stand)

This design is a modular system to hold things securely. I designed it to use in electrochemical experiments and it is inspired by lab stands (statifs). It is also helpful for soldering or any cases you would use a 3rd hand. You may watch this video for a quick introduction to this system: https://youtu.be/XsCk5LUepSI

This system is designed primarily to be very stiff, versatile and cheap. I designed it around 4 main types of elements:
- Base plates to provide stability and strong attach points
- 8 mm bars
- Connectors to rigidly assemble the bars
- Clips of different types to hold any object you are working with

For some applications it is possible to use 3D printed bars, however i prefer to use 8mm stainless tubes with 6mm inner diameter (1mm walls). Such tubes provide an excellent balance between high stiffness, medium weight, medium cost and excellent durability. I have prepared a variety of sizes and it works well for kg range loads on up to 40cm long tubes.

Besides the tubes