Genuine Gerber 99-770 Flapper Used in several Toilet Models. It has the extra hole on the underside unlike the 99-788. The flapper Measures about 3 and 5/8 inches across. Other variances of the part number are G0099770, 99770, 0099770, 99-770 UPC: 671052041848.This flapper also takes the place of the Gerber 99-827 flapper.G0099827. 99827, 0099827.