It is known that a closed, orientable, simply-connected 4-dimensional manifold X' which is an exotic copy of X can be obtained by removing a submanifold C (called a cork) of X and regluing C back. We can assume that C is contractible and the gluing map is an involution. In this paper we define corks and plugs with order p greater than or equal to 2 and we show a plug (P,φ) with infinite order which produces "a crossing change" of Fintushel-Stern's knot surgery where (P,φ²) is a (generalized) cork with infinite order.