Some spark plugs have the word SOLID in their name which means the terminal type is solid as opposed to removable nut

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and full plastic coverage

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while the square bead wires improve casing rigidity

AXP Racing - Skid Plate PHD (6mm Thick) for Gas-Gas EC450F-EC500F-MC450F-ES500-EW500F-EX450F 2024-2025 Options:Black Some spark plugs have theDesigned for motocross, super cross and classic enduro use Weight: 0. 8kg 6mm thick HDPE plastic Protects the subframe, the engine, the crankcase from projections Plastic is 30 to 40% lighter than aluminum HDPE does not generate vibration, does not undergo deformation and absorbs impacts