It's a Stacking Header for Raspberry Pi A+ Pi Model B+ Pi 2 Pi 3 - 2x20 Extra Tall Stackable Header 2 Spacers. 2 Stack multiple plates, breakouts etc onto your Raspberry Pi with this 2x20 female header. The female header part has total 24mm extra tall: when placed on your Pi, a PCB will clear the Ethernet and USB jacks. Plastic height is 8.5mm, pin length 10.5mm so that when a standard 1.5mm thickness PCB is installed, there will be remaining plenty to plug into.