Chevrolet Gen III, IV, and V engines typically run 1.300" diameter dual springs when running aftermarket cams, yet there's currently only one spring height mic available for them on the market. The new BTR spring height mic 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. Unique top with indentations for your fingers which makes it much easier to tighten as opposed to the industry standard knurling on the top. Lazer etching on a black background that's easier to see than the currently available height mic.