A staple cartridge assembly for use with a surgical stapling instrument including an anvil, wherein the staple cartridge comprises: a cartridge body, comprising: a proximal portion; a distal portion; an elongate slot extending between the proximal portion and the distal portion; a bottom surface; a cartridge deck on an opposite side of the cartridge body from the bottom surface, the cartridge deck comprising: a first deck surface; and a second deck surface laterally offset from the first deck surface in a direction away from the elongate slot, wherein the first deck surface is stepped up from the second deck surface relative to the bottom surface; and staple cavities on opposite sides of the elongate slot; staples deployable from the staple cavities into tissue captured between the cartridge deck and the anvil; and staple drivers (602, 603, 604) which support the staples and which are movable from a starting position to deploy the staples into the tissue; wherein the staple cavities comprise deformable retention features which protrude or project from the staple cavities; and characterised in that the deformable retention features are configured to provide a friction fit between the staple drivers (602, 603, 604) and the staple cavities that maintains the staple drivers (602, 603, 604) at the starting positions, but can be overcome by a staple deployment force. a cartridge body, comprising: a proximal portion; a distal portion; an elongate slot extending between the proximal portion and the distal portion; a bottom surface; a cartridge deck on an opposite side of the cartridge body from the bottom surface, the cartridge deck comprising: a first deck surface; and a second deck surface laterally offset from the first deck surface in a direction away from the elongate slot, wherein the first deck surface is stepped up from the second deck surface relative to the bottom surface; and staple cavities on opposite sides of the elongate slot; a proximal portion; a distal portion; an elongate slot extending between the proximal portion and the distal portion; a bottom surface; a cartridge deck on an opposite side of the cartridge body from the bottom surface, the cartridge deck comprising: a first deck surface; and a second deck surface laterally offset from the first deck surface in a direction away from the elongate slot, wherein the first deck surface is stepped up from the second deck surface relative to the bottom surface; and a first deck surface; and a second deck surface laterally offset from the first deck surface in a direction away from the elongate slot, wherein the first deck surface is stepped up from the second deck surface relative to the bottom surface; and staple cavities on opposite sides of the elongate slot; staples deployable from the staple cavities into tissue captured between the cartridge deck and the anvil; and staple drivers (602, 603, 604) which support the staples and which are movable from a starting position to deploy the staples into the tissue; wherein the staple cavities comprise deformable retention features which protrude or project from the staple cavities; and characterised in that the deformable retention features are configured to provide a friction fit between the staple drivers (602, 603, 604) and the staple cavities that maintains the staple drivers (602, 603, 604) at the starting positions, but can be overcome by a staple deployment force.