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Leonard Air Cooled T18 (typically 18mm) spark plugs are vintage components produced around the 1930s to 1950s featuring a distinct multi-ground or vented design engineered to dissipate heat quickly and resist oil fouling.Historical Applications & UsesHistorically, these high-compression, heavy-duty plugs were widely utilized across several applications:
• Automotive: Pre-war and mid-century consumer cars and commercial trucks.
• Agricultural Equipment: Vintage tractors, including older John Deere and Farmall models.
• Motorcycles: Early high-performance and air-cooled motorcycles, particularly vintage Harley-Davidsons.
• Industrial & Marine: Stationary industrial power units and early marine or aircraft enginesgreat automobile history to display
