The Tillotson Standard Volume or what is known as the single stack or gas diaphragm cover plate is the bottom plate or the plate closest to the body on the Tillotson carburetor. 

The diaphragm cover plate covers the main metering diaphragm as the name suggests. It also has the pump diaphragm on the other side of the plate. 

The standard volume plate does not hold or pump as much fuel as the high volume(double stack, Alky) plates. Therefore, we do not recommend using these plates for methanol or for large displacement gas engine.

This plate does not interchange with the high volume(double stack, Alky) diaphragm cover plate. The design of both fuel pump stack are exclusive to one another and cannot be interchanged. Check your carburetor and carburetor listing before ordering.

91A-275 OE Tillotson Standard Volume(Single Stack, Gas) comes stock on HL-1A, HL-129E,HL-132H,HL-166B&C,HL-189F,HL-227A,E,HL-229A,HL-321E,HL-232A,E, HL-250A,B,C,D,E, HL-274E,HL-,292G,HL-293A,F,HL-299E,,HL-334A,AA,B,AB, WX, WXA, WXG,HL-357A,B HL-360A,HL-383A,HL-384A&B, HL-385A, HL-388A,HL-395A, HW-10A,B HW-11A,B HW-12A,HW-17A , HW-22A, HW-23A, HW-27A, HW-30A, HW-31A, HW-32A, HW-33A, HW-34A, HW-35A, HW-43A, HB-10A, HB-11A, HB-12A, HC-102A, HC-103A,HC-112A, HM-1A, HM-2A, HM-12A, HX-10A, HX-12A