Automotive Suspension & Steering Systems, Thrid Edition wrote:Flanges are made with different heights and curvatures to match the tire bead configuration. Flange type is designated by a classification system using one or two letters. The most commonly used flange heights are J= .68"(17.3mm), JJ=.69"(17.5mm), JK=.71"(18mm), K =.77(19.5mm), and L = .85"(21.6mm).