This Buna-N (aka "Nitrile") rubber gasket, P/N 0015-00423, fits many standard SAE 5-hole fuel senders and gauges in addition to those manufactured by Rochester Gauges.
Gauge models include, but are not limited to:
6700 series, 6741, 6743, 6781, 6783, 8700 series, 8741, 8743, 8740, 8780, 8781.