Developed exclusively for Zodiac by TP Developments and made from high grade alloy steel. These tappets are precision machined, than heat treated and finally ground to less than .0002" total readings at a 16 finish. They are called "Fat Axle" because they feature an extra thick roller pin and extra thick rollers for increased roll strength and will not deform, even when used with extreme high lift cams. Inside the tappet is a hydraulic cylinder which is also hardened and hand fit to .0002" using an air gauge. Strongly recommended when using a Performance cam as they give zero valve lash, and zero hydraulic collapse. These tappets are extremely competitive priced but still are the best money can buy. Fits Evolution Big Twin 1984-1999 and Evolution Sportster 1986-1990. Available in stock .8425" diameter and sold each.