The Toyotomi 20477051 is a genuine Bleeder Screw for HC-20, HC-20B, HC-190, HC-190B. Air bleed screw for the convector coil. Use it to purge trapped air from the hydronic loop so the convector heats evenly.
This is an OEM Toyotomi part, so it fits and performs the way the original did. Confirm your heater model before ordering; the model is on the rating label on the unit. If you are not sure which part you need, Rural Energy support can check it against your model and serial number.
Rural Energy is a Toyotomi distributor and keeps HC-20 and HC-190 heat convector parts in stock for fast shipping to dealers and homeowners.