OMC 21 Micron Fuel Water Separator Filter | Sierra 18-7846 Replacement spin-on fuel filter with OMC threads removes contaminants & water from incoming fuel. OMC thread fuel filter Protects marine engines by filtering water, dust, and dirt in fuel supply 21 micron filtration Used on many different OMC engines Replaces Crusader 98041 Replaces OMC 502905 Replaces Mallory 9-37803 Replaces Sierra 18-7851