Capping assemblies (2) of the type fitted to capping units (Ia) in a machine for packaging containers filled with fluid or powdered products are equipped with a gripping apparatus (1) comprising a gripper (4) with three arms (5), each carrying an adapter (20) furnished with a pad (20b) offered in direct contact to the cap, through which the gripping action is applied. Each adapter (20) is securedto a fitting (17, 18) insertable into a socket (16) afforded by the bottom of a structural member (6) that forms the main part of each arm (5) and is hinged to the movable head of a relative capping assembly (2); when inserted into the structural member (6), the fitting (17, 18) is retained automatically by a snap lock mechanism (12) incorporated into the arm (5), which can be released subsequently by introducing the tip of a screwdriver into a slot (18a) created in the side of the fitting (17, 18) and levering the components apart.