An exchange blade knife includes a replaceable blade, a blade holder and a blade lock. The replaceable blade includes an opening adjacent to its base edge. The blade holder includes a blade recess for receiving the replaceable blade and a boss corresponding to the opening in the blade which projects from the surface of the blade recess. The boss has a low portion that is no thicker than the replaceable blade and a raised portion that extends above the surface of the replaceable blade. The blade lock pivots on the blade holder between an opened position for receiving the replaceable blade and a closed position for retaining the replaceable blade. The blade lock also includes an opening for receiving the boss of the blade holder.