Flushmate 503 Series for model M-101526-F3, with serial numbers; F3A, F31A, F3AR, F3C, F3E, F3ER, F3G, F3G2, F3K1, FMK2, F3L, F3LR, F3R, F3M, F3MP, F3MR, F03, F3U, F3UR, F31, F34. Does not fit Kohler K4404, and Gerber 28-385. Use part# SX-0446328 for Kohler K4404 Use part# SX-0446336 for Gerber 28-385