A universal Wi-Fi router stand for routers 20x10cm and bigger that allows for proper ventilation. 

Router on the photo is a 260x135x39 mm TP-Link Archer AX50 which suffers from overheating if not elevated. 

Has been tested on a layer width of 0.3 mm, but it is of little importance in this particular model. I used PETG and recommend using high-temperature filaments.