Promura filters

Hello.

Recently I bought 210/5.6 Symmar-S and finally it arrived. And it had Promura Skylight(1A) filter.

As for me, I use either b/w filters or polar, but never skylight. And just quirious. Who's that "Promura"? Hardly any info on web. Worse it having on lens or just let it go in my "photo box", where I store all minor, rarely used items?

Probably japanese, like Sun. Seem to have made (badged) a range of wide/tele adapters as well as zoom lenses. Keeps the top surface of the symmar free of dust/fingers etc.