That’s fuel drain/shut off valve. There’s a screen built onto that valve that is inside of the fuel tank. If there’s a inline fuel filter on the tractor, it will be downstream from that valve.
Is the valve functioning? To test, close the valve and remove the fuel line. Have a container ready to catch the fuel and open the valve. If you have a good flow, nothing is wrong and you can put your fuel line back on.
Tell us the problem that you are having.
Give us the complete model and serial numbers of your machine.