I ordered the wrong fuel flow sensor initially - ordered the red cube. Turns out, with a gravity feed fuel system - you need the gold cube to make sure you meet the FAA requirement of 150% maximum fuel flow to the engine. The gold cube has a larger orifice and therefore flows more fuel. The red cube might be more accurate at idle conditions - but the FAA requirement is mandatory - so, Michigan Avionics exchanged this for me - thanks!