an anvil assembly having a housing and two rotatable inserts with flat upper surfaces against which the heated shoes of a package sealing machine may press a covering sheet onto a plastic package tape . the inserts have a limited range of rotation so that they automatically align themselves to be parallel to the heated shoes when they are contacted thereby . this rotatable insert feature obviates the need for precise , laborious alignment efforts . alternatively , a pair of rotatable blades are pivotally attached to the shoes and act against a fixed anvil surface , thereby automatically aligning themselves to be parallel to the anvil surface .