I’ve recently encountered spring-loaded pogo pins for PCB testing.

There are short pins, the size of typical pin header; but they are relatively expensive, so you have to use them sparingly. They are also designed to fit 2.54mm grid, so not suitable for super-tiny projects (as my BLE board).

And then there are long ones.

They come in mostly 3 sizes: P50, P75, P100. I tried P50 and P100. P50 I need to program my BLE RC board, they are 0.68mm diameter. As they are so tiny, I don’t see any other uses for them, it’s even hard to disassemble them without damaging. It also bends very easily, one was bent during shipping or by seller. But they come in packs of 100 and are so cheap that it doesn’t matter.

P100, on the other hand, are larger, 1.67mm outer diameter, 1mm needle diameter. It can be disassembled (destructively), and spring can be used for projects. Outer tube and central rod can also be used.

Search "pogo pin P100" on aliexpress if you are interested.