Large hex original design for air cooled engines #3 heat range terminal nuts and seal washers included. Includes top ventilated brass collars for cooling as original Doering design! Terminal nut is removable. Plug set has a round feeler gauge. Spark plugs have a 18mm thread and the large hex measures 1-3/8 which is perfect for early restoration and riding. Set is for use with 1924 Harley models that require 7/8 thread spark plug. *NOTE: Sold as a pair. *NOTE: Fits early Knuckleheads that can accept the 1-3/8 large hex. *NOTE: Air cooled spark plug set features a nickel plated full size hex. Full size hex is for single and twin flat heads For IOE types with space for the large hex. Doering Spark Plug Company was founded in Brooklyn NY in 1918 making plugs for tractors. In the later years they made plugs for automotive applications for motors that burned an excessive amount of oil. They are manufactured to the original standards of that era but not in Brooklyn any longer.
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