1/2" conduit (emt) tee

thingiverse

This connector is designed for easy assembly of small projects, like greenhouses or a plastic-covered cab frame for snowblowers. More infill means greater strength and durability. You'll need two connectors per joint to secure the connection. They can be pressed together or secured with screws. Note that the press fit can be tight on some printers, requiring extra force to separate them. These connectors were originally designed for printing in PLA material.