Enhance the performance of your 1970-1976 GM 250 4.1L engine with this set of 6 Autolite 147 spark plugs. Made of high-quality copper material, these spark plugs have a thread diameter of 14mm and operate at a voltage of 12V. They are compatible with R46T and ARF8 interchange part numbers and OEM part number 5613357. These spark plugs are suitable for gasoline fuel type and have a standard configuration. They are not vintage parts and do not come under the category of performance parts. Buy these reliable spark plugs from Autolite, a trusted brand in the automotive industry, and enjoy a smooth driving experience.