1. Technical Bulletin Bulletin No PRO 06 02 Effective Date 4 15 81 Page 1 of 1 Subject PH 2 Air Horns In early 1979 the threads on air horn bells were changed from a 4 28 Thread fine to a 3 10 Thread coarse For service requirements both the fine and coarse thread bells are available Piece numbers are listed below Please note on catalog page 06 A 1 3 28 3 10 Fine Thread Coarse Thread Long Bell Chrome 212678 293515 Long Bell Unpainted 239792 293516 Short Bell Chrome 212679 293518 Short Bell Unpainted 239793 293519