Abstract: A gauge for determining the proper formation of an annular recess formed at the bottom of a blind bore in the body of a hydraulic lash adjuster. A shaft having a tapered end is mounted in a block and an expandable, cylindrical gauging member is received over the tapered portion. A cylindrical sleeve is received over the shaft and is biased into engagement with the gauging member by springs acting between the block and the sleeve. When this assembly is inserted into the lash adjuster body and the gauging member contacts the bottom of the bore, continued axial movement of the shaft causes the gauging member to expand into the recess as the tapered portion of the shaft moves through the gauging member. Measurement of the amount of movement of the shaft provides an indication of the radial movement of the gauging element by virtue of the tapered interconnection.