A tool assembly comprising: a cartridge assembly ; a shell housing the cartridge assembly and defining a passage ; and an anvil assembly including an anvil and a center rod extending from the anvil, the center rod defining a longitudinal rod axis (A-A) and including an alignment portion sized to pass through the passage, the alignment portion including a first spline and a second spline , each of the first and second splines extending in a direction parallel to the rod axis, the first spline having a first leading portion and the second spline having a second leading portion , the first leading portion positioned along the rod axis proximal of the second leading portion, wherein the first spline includes a first spline body extending from the first leading portion along the rod axis having a first length (L 1 ) and the second spline includes a second spline body extending from the second leading portion along the rod axis having a second length (L 2 ) less than the first length ; wherein the alignment portion has a plurality of faces defining a polygonal cross-section transverse to the rod axis (A-A); wherein the first spline is disposed on a first face of the plurality of faces, the first face having a first width less than a width of adjacent faces, and the second spline disposed on a second face of the plurality of faces, the second face having a second width less than a width of adjacent faces; and furthermore wherein the shell includes alignment splines extending along an inner wall of the shell defining the passage , and the first leading portion being configured to engage the alignment splines to clock the anvil assembly relative to the cartridge assembly as the center rod passes through the passage of the shell. a cartridge assembly ; a shell housing the cartridge assembly and defining a passage ; and an anvil assembly including an anvil and a center rod extending from the anvil, the center rod defining a longitudinal rod axis (A-A) and including an alignment portion sized to pass through the passage, the alignment portion including a first spline and a second spline , each of the first and second splines extending in a direction parallel to the rod axis, the first spline having a first leading portion and the second spline having a second leading portion , the first leading portion positioned along the rod axis proximal of the second leading portion, wherein the first spline includes a first spline body extending from the first leading portion along the rod axis having a first length (L 1 ) and the second spline includes a second spline body extending from the second leading portion along the rod axis having a second length (L 2 ) less than the first length ; wherein the alignment portion has a plurality of faces defining a polygonal cross-section transverse to the rod axis (A-A); wherein the first spline is disposed on a first face of the plurality of faces, the first face having a first width less than a width of adjacent faces, and the second spline disposed on a second face of the plurality of faces, the second face having a second width less than a width of adjacent faces; and furthermore wherein the shell includes alignment splines extending along an inner wall of the shell defining the passage , and the first leading portion being configured to engage the alignment splines to clock the anvil assembly relative to the cartridge assembly as the center rod passes through the passage of the shell. <EOS>