Cable Gland - Waterproof RJ-45 / Ethernet connector [RJ-45] : ID 827 : $7.95 : Adafruit Industries, Unique & fun DIY electronics and kits
ASI 3001319 Waterproof M25 Plastic Cable Gland with Locknut, M25 Thread,10mm to 17 mm Clamping Range, Light Gray (Pack of 10): Amazon.com: Industrial & Scientific