Expensive and should have come with the trijicon rmr - Trijicon RM63 RMR Mount Sealing Plate

I needed this to mount to my new MOS Glock 19. I bought the sight when it was on sale and I did not notice that this attachment was not included. The plate was $15.00 or so but the shipping was over $7.00! Lesson learned by me. I have not installed it yet, I am waiting for my new Gen4 Glock 19 that I won at a GSSF match.