Perfect if you are using a trijicon rmr sight - Trijicon RM63 RMR Mount Sealing Plate

I bought this along with the Trijicon RMR for my custom Glock 17. This Glock has the full Shadow Systems upgraded slide and barrel. While the Trijicon RMR would have fit nicely in the slot on the Shadow Systems slide, this sealing plate makes the whole thing more secure and safe, and adds much more moisture protection. It is easy and intuitive to install. More importantly, this works perfectly. This is a small thing. But skimping on this item when you've spent so much money on the handgun, the customization and the Trijicon RMR is penny smart and pound foolish. Totally worth it.