Use this set for class lights on most EMD hood units and GE U-Boats. Fits Detail Associates headlights #229-1017, 1018, 1019 and 1020 (sold separately). Drop-in mount for marker light castings from Cal-Scale, Precision Scale and most HO Scale steam locos. Can also be used as recognition/formation lamps on aircraft kits in various scales. Actual size: .052", Drill #55.