The Fruitland RF-U-Seal bulkhead washers are parts for a Fruitland Vacuum Pump. It is designed to stop oil leaks at the top of the oil tank seal housing between the seal housing and bulkhead fittings.
The U-Seal will fit several different Fruitland Vacuum Pumps RCF250, RCF370, and RCF500. The U-Seal will as fit the Cowboy Pump CVP620 and CVP700 vacuum pumps. This item is priced and sold as a pack of 4 seals.
This is part #18A on the RCF370 pump exploded view and part #18A on the RCF500 pump exploded view.