This is a T-Connector for an eBay Chinese K40 Laser cutter and engraver. Designed with a ~7mm OD an and a ~3mm ID. The idea is this will be used with a small pressure sensor to detect the flow of water on the exist side of the tube. My suggestion would be to connect the outbound supply to the straight inlet and the pressure sensor to the opposite side while the “T” side is used for the exit flow back to the bucket. This way, there is a greater amount of “pressure” applied to the sensor ensuring it is properly tripped as the pump (at least the one which came with the unit) does not provide that much pressure.