The M-20 Air/Oil Separators for crankcase breathers have set the performance standards for aviation. A simple performance test for any separator is to fill the engine oil to the full mark and take a 2 hour flight. Only with the M-20 will the oil still read full with none blown out on the belly. This difference makes them preferred over all others. Only the M-20 Separators carry FAA approval for all 1600 makes and modelos of certified piston aircraft from 45 hp to 950 hp. They are also applicable to all homebuilts and foreign made aircraft with similar power.

No vacuum pump connection is used, since the addition of as little as 1/16 PSI will make a new engine perform like it is run-out. M-20's vent the crankcase pressure and use only gravity for returning the oil.

The -A and -B suffix varies only in the direction of the oil return tube. On the -A models the direction is away from the inlet, on the -B towards the inlet. The -A's generally favor Lycoming, Franklin and radials, the -B's favor Continentals. Either may be mounted in-line; the -B may also be firewall mounted since it has a blank side.

Model 605Y "Y" fitting