A fastener cartridge assembly for use with a surgical end effector. The fastener cartridge assembly can comprise a cartridge body (5650), fasteners, and a layer of material releasably secured to the cartridge body. The layer of material can be a tissue thickness compensator (5658). The cartridge body, the fasteners, the tissue thickness compensator and/or the end effector can comprise various features to releasably secure the tissue thickness compensator relative to the cartridge body. For example, the cartridge body can comprise slots (5656), projections (6048) , cavities (5948), drivers (5920), locks (6320), and/or keys (6353), the fasteners can comprise barbs (6296), and/or the tissue thickness compensator can comprise mounts ((5660),(5760),(5860),(5960)) and/or connectors (6480).
