Abstract: A lash adjuster is provided which can maintain stable valve lift. An adjuster screw is mounted into a threaded hole formed in the bottom of the end plate of a lifter body. An elastic member is mounted in the threaded hole to bias the adjuster screw axially downwardly. The female threads of the threaded hole and the male threads of the adjuster screw are serration-shaped. A plurality of axial grooves are formed in the inner periphery of the threaded hole to circumferentially divide the female threads into many separate portions, and satin-finished rough surfaces are formed on the pressure flanks of the male threads by shot-peening to enable quick expulsion of oil film disposed between the opposed pressure flanks, thereby stabilizing the valve lift.