Most likely a CVI Zero Order 1/2 Waveplate as it has the Orange and black markings for fast and slow axis typically on their product. I don't know the make for sure as it is a pull from a polarizer rotator. 

This is a 1/2 wave Zero Order Achromatic waveplate for visible lasers. 

Tested with  488, 532, 589 and 635nm in a rotating mount into a polarized visible beam splitter cube. 

It's great with 632.8 and 635nm, pretty good with 589nm and 532nm. not good with any blue i tried.

So I'm calling it a "semi-achromatic" waveplate. Zero order are the preferred type for many applications that require repeatability, temperature stability and wide acceptance angle.  

The optic itself is 2 plates optically contacted together 

The assembly is 1/2" diameter.

I combine ship to keep costs down.