tappet(n = noun.artifact) - a lever that is moved in order to tap something else;
is a kind of lever
A lever or projection moved by some other piece, as a cam, or intended to tap or touch something else, with a view to produce change or regulate motion. G. Francis. [1913 Webster]
tappet, n. a lever or projecting part used in machinery to give intermittent motion, often in conjunction with a cam.
Etymology:
app. f. TAP(2) + -ET(1)