Abstract: An insert filter designed for press-fitting into airway port of hardware apparatus of a railway air brake system whereby the airway ports have at least two different diameters, the insert filter having a ring member defining an opening, a plurality of spaced support ribs extending from a first side of the ring member and intersecting at a location spaced from that first side of the ring member, and a screen mesh supported by the plurality of spaced rib supports defining a volume adjacent to the opening through the ring member. Each of said support ribs having a primary interface rib surface adjacent to an outer edge surface of the ring member adapted to engage inner edge surfaces of a larger, first airway port, and a secondary interface rib surface adjacent to the primary interface rib surface adapted to engage inner edge surfaces of a smaller second airway port.