An operating cam for use with a hardness tester may comprise: first and second cylindrical journal portions for respective disposition with first and second cylindrical holes provided through a housing of the hardness tester; a substantially cylindrical cam portion of smaller diameter between the journal portions and the axis of which is eccentric to the axis of the journal portion; an end portion adjacent the second journal portion having a common axis therewith and engageable for rotating the cam member about the common axis between no load, minor load and major load positions; and stop portions adjacent the end portion engageable with corresponding stop portions on the tester housing for limiting rotation of the operating cam between the no load and major load positions.