A tool assembly for use with a surgical instrument, the tool assembly comprising: an end effector (154) that includes a first member (330) of the jaw and a second member (340) of the jaw, at least one member of the jaw is movable with respect to the other jaw member between the separated and approximate positions, the first jaw member includes an upper surface (332) of contact with the tissue and a lower part (334)； an immobilizer member (370) disposed adjacent to a distal part of the first jaw member, the immobilizer member is pivotable with respect to the first jaw member between a first position where at least a part of the immobilizer member is located outside the first jaw member (330), and a second one in which the relative movement of the jaw members (330, 340) towards the approximate position causes at least a part of the immobilizer member (370) to move towards the first member of the jaw (330)； and a skate (400) that travels along the tray (334) of the first jaw member (330), wherein the skate (400) includes a plurality of cam wedges (402a, 402b, 402c, 402d), and wherein each cam wedge is connected to an adjacent cam wedge by a transversely arranged connecting member (404), characterized in that said lower tray portion (334) includes a groove (336) disposed therein and at least a part of said immobilizer member (370) is located within the groove (336) when the immobilizer member (370) is in said second position； and said connecting member (404) is disposed adjacent to a proximal part of the skate so that a distal part of each of the cam wedges (402a, 402b, 402c, 402d) is cantilevered from the connecting member ( 404) and the cam wedges (402a, 402b, 402c, 402d) define a space in which the immobilizer member (370) is arranged when the skate (400) is disposed at the distal end of the first jaw member (330 ).Un conjunto de herramienta para usar con un instrumento quirúrgico, comprendiendo el conjunto de herramienta: un efector extremo (154) que incluye un prim
