SG-102  is a flow monitor for the purpose of monitoring the flow of fluid without indicating the flow rate.  

The connection part is screwed and you can observe the color tone of the fluid and the mixture of bubbles through the sight glass on both sides.  Also, compared to the screw type, the installation is simple and the range of specifications is wide.  It is divided into ball type and flapper type according to the flow monitoring method inside the glass.