401497 Hoffman Model 77 Water Vent Valve. Bell & Gossett Water Vent Valve, #77.

For efficient releasing of air in hydronic heating systems, such as baseboard radiators, convector radiators and small heating units.
1/8″ NPT straight shank.
Maximum operating pressure: 50 psig (3.5 bar).
Maximum temperature: 240°F (116°C).