These plugs fit ford 6.4L diesel engines only. Premium dual-element, self regulating glow plugs. (Set of eight). **100 Degrees hotter & 20% faster** made for us by wellman usa. These updated plugs offer a noticeable improvement in cold weather starting. They get 100 degrees hotter and do it in 20% less time than the oem plugs. These updated plugs offer a noticeable improvement in cold weather starting. They get 100 degrees hotter and do it in 20% less time than the oem plugs. Anyone that has been through a winter with their 6.4L ford diesel knows these engines don't start very well in the cold. These plugs help cold weather starting considerably! Check out the test results of the side-by-side comparison pictures. (Wellman plug is on the right) both plugs were new, both powered from the same battery at the same time, with the same size wire. - Wow - look at the difference! In addition, the seal that holds the combustion chamber pressure back incorporates an internal o ring instead of just the clamped metal-to-metal seal as on the oem plug. This means increased durability and the elimination of combustion seepage through the plug housings. Considerable design effort has been put into these new plugs to ensure that they not only start better, but have improved service life. Special attention has been paid to the plug tips in order to minimize potential swelling that can occur as the plugs age. Some lesser plugs can swell so big at the tip, that they won't come back out of the head, that's a problem you don't need. Tested two times at the factory before shipping. Pricing is for the complete set of 8. Made in shelbyville, indiana, usa. Warranted for one full year.