To ensure compliance with new interchange rules imposed by the Association of American Railroads, many railways in the early 1940s to mid 1950s converted freight cars with K-Brake systems (generally - but not always - identified by a vertical brake staff) to A.B. Brake systems. To identify these cars while in interchange service the cars where stencilled on both car sides with the words:"A.B. BRAKES" As location of this stencil varied by railway (and often by car series or type) please consult prototype photographs for accurate stencil locations.