A bypass-style regulator specified for carburettor use, with three AN6 ports for feed, outlet and return. The carburettor distinction matters: a carb needs low pressure, because anything much above what the needle and seat can hold simply pushes past and floods the bowls, causing rich running and fuel smell at idle. A bypass design keeps fuel circulating back to the tank rather than dead-heading against a closed valve, so pressure stays stable instead of spiking as the engine comes off load and the fuel in the line stays cooler. Suits mechanical or electric pump setups on carburetted engines. Set final pressure with a gauge fitted at the carburettor.