To provide a surgical instrument for clamping, resecting, and/or joining a tissue.

An end effector comprises an anvil shaft, a first anvil assembly disposed at a distal portion of the anvil shaft, and a second anvil assembly mountable on the anvil shaft proximally the first anvil assembly, and the anvil assembly and the anvil shaft are arranged by a keyed slot. The first anvil assembly has a plurality of first anvil pockets arranged in a practically circular line, and it deforms a fastener ejected from a first fastener cartridge.