Description Piston o-ring type, 2-1/2" O.D. Tractors: NAA (1953-1954). Optional for 9N, 2N, 8N when used with o-ring NAA533A & NAA473A. This item is a suitable alternative for the following: NAA530B, 1101-1051, 11011051, A-NAA530B, ANAA530B