0.4mm diameter nozzle cleaning needle. Works well for clearing minor jams on hot end nozzles 0.4mm and larger. 

0.4mm and 0.3mm are commonly found on most printers such as the Creality Cr-10, Wanhao Duplicator i3 and others.

For proper usage, heat hot end up to the temperature for the filament that was clogged and carefully insert the needle into the tip of the nozzle. As the needle is quite thin, care must be taken to ensure the needle is not bent or broken as it’s inserted. Move the needle up and down through the nozzle a few times, and then try extruding filament again.

For more stubborn clogs, a nozzle cleaning drill may also work well.