I thought these were little passive Q switches at first, (the kind that are attached to the end of YAG rods).

These are High Reflectors that can take Q switched pulses @ high energy. 

They might be used as the HR of a laser rod cavity and installed at the end of a YAG rod. 

AR coating looks nice for it being old stock.  I will test with 1064nm soon and post my findings to be sure it is for 1064nm. 

Sale is for one and it will come in a suitable container. I have 23 for sale. 

I combine ship to keep costs down.