A tool assembly includes a cartridge assembly, a shell, and an anvil assembly. The shell houses the cartridge assembly and defines a passage. The anvil assembly includes an anvil and a center rod extending from the anvil. The center rod defines a longitudinal rod axis and includes an alignment portion that is sized to pass through the passage. The alignment portion includes first and second splines that each extend in a direction parallel to the rod axis. The first spline has a first leading portion and the second spline has a second leading portion. The first leading portion is positioned along the rod axis proximal of the second leading portion.
