Trimmer Head Bump Knob / Ryobi 791-180814 BPack Size:1Ryobi 180814, Ryobi 147496, Ryobi 791-180814 BGreen Meadow VBH992, NHC 207-2481, Oregon 55-812, Sunbelt RY-55812, Sunbelt B1RY55812Ryobi IDC 395, 580, 580-1 and 780; Ryobi series780R, 790R, 865R, 885R, 990R and SingerGBC2818 2" OD x 15/16" HT, 3/8"-16 LH external thread size