4″ diameter tri-clamp glass viewing window. A flashlight can be sourced separately to see inside the boiler.
All Mile Hi boilers 16 gallon size and above will include a 2″ port near the lid on the kettle. The viewing window is designed to install and clamp down to that port so fluid levels can be seen.
This is great for stripping runs that wouldn’t utilize the full volume of the boiler or for informational purposes on your heating element or boiler liquid.