BTR GEN III HEMI Valve Spring Height Mic For 2003-later 5.7L 6.1L 6.2L 6.4L Hemi Dodge Chrysler Jeep Engines Brian Tooley Racing's spring height micrometer for Gen III HEMI engines has several design changes that make it superior. These include more desirable .100" height change per revolution which reduces the chances of reading errors associated with spring height mics that have .050" height change per revolution. It features a unique top with indentations for your fingers which makes it much easier to tighten as opposed to the industry standard knurling on the top. Laser etching on a black background ensures easy measurement readings.