Could someone please help me ID this odd 4x4 filter I got?

[nickmilo]

This oddball filter came in a lot of filmmaking equipment I just bought, and (please excuse the newbie question) but I was hoping someone could help me identity it? Fits perfectly in a 4x4 filter tray... most of my filter experience is limited to ND's and color corrections, pro-mists, etc... nothing too fancy, so I was hoping a seasoned DP out there could help point me in the right direction for some specs on it? Wanted to find some specifics on it so I know exactly what I got (and how I can properly utilize it) I was thinking it was an odd piece of glass that was re-purposed as a close up 4x4, but if you guys have seen it before and could shed some light, that'd be much appreciated
cheers!
Nick

 

[David W. Jones]

Is it a + diopter

 

[nickmilo]

Ask a question, get an answer! ...thx, yes, looking them up, it seems to be a diopter... the fact that its square and not round is throwing me off.... More convenient if you ask me! ...time to start testing

 

[Nick Gardner]

I'll buy it from you, or trade you a set of 3 tiffen 72mm diopters for it.

Nick

 

[Eric M Hurt]

I'll buy it if you want to get rid of it. PM me.