Genuine Gerber 99-788 (2 pack) Flapper Used in several HET High Efficiency Toilet Models. It does not have the extra hole on the underside like the 99-770. The flapper Measures about 3 5/8 inches across the top. Other variances of the part number are G0099788, 99788, 0099788, 99-788, 99 788, 99788,G0099833, 99833, 99-833. UPC: 671052049400