🔍 Key Concepts

• Look closely at how parts D and M are positioned between the metal body pieces – they form the clear passage where you actually see the water level. • Think about what transparent, pressure‑resisting piece is installed in a boiler gauge or water level indicator so you can visually observe the fluid. • Consider which option names a solid, clear component rather than a soft gasket or a thin protective film.

💭 Think About

• Are D and M drawn as soft sealing material, or as a solid, transparent block that the operator looks through? • On a boiler water level gauge, what is the common name of the clear part that is clamped between the metal faces of the gauge body? • Which answer choice best fits a rigid viewing element, as opposed to something used only for sealing or protecting another surface?

✅ Before You Answer

• Verify in the illustration that D and M appear clear/transparent and rectangular, indicating a viewing element. • Check which options would realistically withstand boiler pressure and temperature while providing a clear view of the water level. • Confirm that the remaining parts that look dark and compressible are more likely to be gaskets, not the items labeled D and M.