The “Donut” cooler fits between the oil filter and the engine block. They are available in 2 sizes: 48 and 57 mm thick. An extension bolt with 3/4”-16 UNF thread is supplied. The cooler has 16 mm water connections that must be connected to your car’s cooling system. This cooler is ideal for off-road conditions where dust or stones may clogg oil-to-air oil coolers.