Unless you have X-Ray vision, it can be hard to see inside of a metal vessel. Whether it be a feedwater tank or a boiler, the water level is critical to its operation and safety. Using a sight glass is one of the best methods to see at a glance your water level. The red line sight glass utilizes a red line running along the glass tube to better highlight where the top of the level is. Useful for liquids that are clear, such as water. This heavy duty glass tube can withstand being in a working environment without letting you down.