Will this fit a Glock 19 MOS gen 5 without having to buy another adapter plate? — 2 Answers

The MOS line of Glocks includes a package of four mounting plates with the weapon in the pistol case. The RMR footprint is plate #2. You can either use the longer screws that hold the factory coverplate to the slide for the adapter plate or use the slightly shorter screws (included in the mounting plate package) to mount that plate to the slide. The Holosun 508t X2 comes with several packs of screws of different lengths with blue Loctite pre-applied. They are #6-32 screws about 5/16" long, BTW, and larger than the threads in the slide for the adapter plates. Install the Holosun 508t X2 to the adapter plate and file/grind the excess screw length so it sits flush with the bottom of the adapter plate and does not try to protrude into the slide. Make sure it does not poke through >at all< but you're maximizing your thread engagement. Once you have that trimmed properly, remove the 508t from the plate, install the plate on the slide and then the 508t to the plate. I would personally add a drop of fresh liquid loctite to the screws between the 508t and adapter plate since it's so thin. The screws from the plate into the slide have lots of thread depth to work with, so I woudn't worry about those. Give it a day to dry and you are GTG.