The Tillotson Body Channel Retaining Ring Hold the Fuel Screen located in the body of the Tillotson Carburetor. 

These screens are used in carburetors that do not use a nozzle check valve as part of the high side fuel circuit. 

55A-212 OE Tillotson Body Channel Screen Retaining Ring fits carburetors: HL-132H, HL-189F, HL-304WX, HL-334WX