Many DIY microcontroller projects require to program / flash the uC (e.g. with a bootloader) before it is useable in the circuit.
Smaller PCB often don't give the chance to access the uC chip at its ISP pins for flashing easily, so the easiest way is to program the uC before soldering it to the PCB.
With this cheap DIY adapter plate you can just do this. Press the uC into the quad hole to contact all 6 ISP pins and it gets contact with the programmer device.
To assemble this unit, just use 6 braid wires and remove all but one copper string at their ends. Wind the thin single wires through the 6 tiny holes at the quad opening and glue the "fat" end into the joint socket on the adapter plate (see pictures).
To program the uC, place it flipped over into the quad hole (the indicator dot tells you the orientation). Check the alignement of the 6 contact wires, then press the uC firmly into the opening to start. The single copper strings make good contact to the uC - it's cheap and simple, but it works!
Printed with 0.1mm step, 0.4mm nozzle and 40% infill. No support structure required.