Fuel tank strainer,screen?

[bruceincam]

The spark arrestor works by exposing any flame to a large number of small surfaces (the screen). A flame front exposed to such a device will get broken up by the screen and as a result cool to below the ignition point and become self extinguishing. In theory at least ----

If you want a better explanation, just search for "spark arrester" and read on --------

Now, full disclosure, I've removed mine because of the difficulties it offers in refueling at the service station. It's hard enough to lean over the fenders and the cowl.