I have this little porcelain insulator here that i can't seem to find any info on. it says P.P.ING on the top and is threaded with smooth base it measures 2 5/16" at the base and is 3" tall

any ideas of what it is worth? also if you know of any good Porcelain sites that have picture id's that you can see at a glance like some of the good glass sites i would appreciate. i have about 200 porcelain home and have no idea how to figure them out.