I have no idea what these things are for, but they seem to be associated with some kind of laser application. They are tiny, less than 1/4" long overall. The box says they are 1/4 wave mirrors, which means the surface is certified to be flat to within 1/4 of the wavelength of the light they are intended to be used with, about 10 microns in the deep infrared.
A claim I find to be somewhat dubious. I mean, just look at the things: Do they look like mirrors to you? Any part of them? If you know anything about these devices, I'd like to hear about it.
Source: eBay seller vanagon
Contributor: Theodore Gray
Acquired: 1 August, 2003