A rotary mower system comprising: a mower disc having a body rotatable about a central axis of rotation, the body including an upper surface and a lower surface positioned beneath and opposite the upper surface; wherein the body extends radially outward from the central axis of rotation and defines an elongated slot passing therethrough, between the upper surface and the lower surface; a retention block attached to and rotatable with the body, wherein the retention block includes a recessed surface positioned against the upper surface of the body and cooperating with the upper surface to define a pocket therebetween, the pocket including a radially outer portion and a radially inner portion; wherein the retention block includes a cover portion at least partially covering the elongated slot over the radially outer portion of the pocket; a pin having a shank portion passing through the elongated slot, wherein the shank portion of the pin is moveable within the elongated slot along a radially extending path relative to the central axis of rotation between the radially outer portion of the pocket and the radially inner portion of the pocket; wherein the pin includes a head portion attached to the shank portion, with the head portion positioned within the pocket between the retention block and the body of the mower disc, such that the cover portion of the retention block at least partially covers the head portion of the pin to prevent withdrawal of the pin from the elongated slot when the pin is disposed in the radially outer portion of the pocket, and wherein the cover portion does not cover the head portion of the pin when the pin is disposed in the radially inner portion of the pocket to allow vertical movement of the pin relative to the body; and a knife positioned adjacent the lower surface of the body and coupled to the shank portion of the pin. a mower disc having a body rotatable about a central axis of rotation, the body including an upper surface and a lower surface positioned beneath and opposite the upper surface; wherein the body extends radially outward from the central axis of rotation and defines an elongated slot passing therethrough, between the upper surface and the lower surface; a retention block attached to and rotatable with the body, wherein the retention block includes a recessed surface positioned against the upper surface of the body and cooperating with the upper surface to define a pocket therebetween, the pocket including a radially outer portion and a radially inner portion; wherein the retention block includes a cover portion at least partially covering the elongated slot over the radially outer portion of the pocket; a pin having a shank portion passing through the elongated slot, wherein the shank portion of the pin is moveable within the elongated slot along a radially extending path relative to the central axis of rotation between the radially outer portion of the pocket and the radially inner portion of the pocket; wherein the pin includes a head portion attached to the shank portion, with the head portion positioned within the pocket between the retention block and the body of the mower disc, such that the cover portion of the retention block at least partially covers the head portion of the pin to prevent withdrawal of the pin from the elongated slot when the pin is disposed in the radially outer portion of the pocket, and wherein the cover portion does not cover the head portion of the pin when the pin is disposed in the radially inner portion of the pocket to allow vertical movement of the pin relative to the body; and a knife positioned adjacent the lower surface of the body and coupled to the shank portion of the pin.