This black, wool, circle felt washer is designed for either the bottom of the drip pan tray or if you prefer, as a black felt to sit atop the spool pin plate. 

The 1" black circle felt is genuine wool and specially cut with a small hole in the center.  The hole appears smaller than the spool pin, but it stretches over the pin and slides down for a proper fit.  This is so the felt doesn't spin with the thread (if felt was too loose), but allows the thread spool to spin by itself on top of the felt's soft, wool surface.