A panel system for covering a lengthwise segment of an elongate firearm mounting rail. The panel system comprises at least one pair of identically shaped panel halves. Each panel half comprises a body having a top, a bottom, an abutting proximal edge and a distal edge. At least one axial tongue extends from the abutting proximal edge and a corresponding axial groove having a groove mouth is defined in the body. A cantilevered clip extends from the abutting proximal edge. A clip receptacle is defined by the body. A proximally extending lip extends from the body bottom near the distal edge. Each panel half is configured so that with the abutting proximal edges brought into abutment, each axial tongue of each panel is received in a corresponding axial groove of the other and each cantilevered clip engages the clip receptacle of the other.