The Hummel 2 532 3800 01 Breather Valve has an external thread size of G 3/8 and is designed to regulate flow, pressure, and vacuum levels in air, gas, or liquid systems. It is a one-way valve that opens when the pressure within an internal system drops, allowing air or gas to flow in, and closes when pressure rises, trapping air or gas. The valve is also factory-set to a specific pressure range to ensure optimal performance. This valve is made of corrosion-resistant metal and rubber materials, making it highly durable and able to withstand a variety of temperature and pressure levels.