I found this at a WW2 training base and I have not been able to find any information on it. On the front it says U-C . I . Corp. (or U-C . F. Corp.). Does anyone know what it is?
It appears to be the front component of one of the varieties of rivet-button. This version is used as a heavy-duty button on "work shirts" and as a pants-waist closure button. See the photos below.
The marking is from United-Carr Fastener Corp., which made snaps for a variety of military items (during WWII and a bit before), as well as civilian. Being found where it was, surely it was from military gear... which could have been almost any canvas or rubber gear with snaps.
And, just for the heck of it, here’s the patent: