A contractor from Maryland says:
May 10, 2016
These plastic pieces are on the exterior of a bow window and hold the IGU in place. They are brittle and crack when we try to remove them. The thickness of the glass is 11/16.
Tom from SWISCO responded:
May 11, 2016
It's hard to tell what you have based on these pictures. Is there any way you can get us a shot from an angle that clearly shows its end? We will need it to be as undamaged as possible, as well. I know yours is very brittle but please try your best. It would be a huge help. In the meantime, check out our selection of window glazing and see if you can find a match here.