Lash adjuster

A lash adjuster comprising a cylindrical housing having an open top and formed with an internal thread on an inner periphery thereof, a screw rod having an external thread formed on an outer periphery thereof and in threaded engagement with said internal thread, and a spring biasing said screw rod outwardly of said housing, each of said internal thread and said external thread comprising a pressure flank configured to receive pressure when a force that tends to push the screw rod into the housing acts on the screw rod, and a clearance flank having a smaller flank angle than said pressure flank, said screw rod having an end protruding from said housing and configured to support an arm of a valve operating mechanism so as to be pivotable about said end, wherein the pressure flank of said internal thread has oil film expelling grooves formed therein to extend in a direction to cross the direction in which said internal thread extends, said oil film expelling grooves being formed using a tap having a thread that extends so as to cross the internal thread.