Schuko type 3 way socket. Perfect for extension cables. Full description below.  

A black rubberised 3 way F Schuko plug assembly with double scraping earth contacts and sprung IP 44 autoclosing cap, suitable for industrial use. Manufactured to DIN49441 and IEC 60884 with standard cable entry. This rubber plug features a double earthing system and will work also with French/Belgian Sockets. 

2-Pole + Earth16A total 250VScrew TerminalsFor connection of cables up to 3 x 2.5mm2With two earthing systemsAccording to CEE7/VIISplash-Proof IP44

Full catalogue detail here https://d5135fc6-0f2d-4f2f-bc18-18a7ba0dba7e.filesusr.com/ugd/83d939_05a0352e6b0d46eba521b750276584bd.pdf