This is a Trijicon Mount known as the Ruggedized Miniature Reflex, model AC32064.
This kit includes the sealing plate and proper screws needed to mount an RMR(R)/SRO(TM) on the Glock(R) MOS slide and the Springfield(R) OSP pistol. For the SRO(TM)" only the screws in this kit are required for proper mounting. One must have this kit to mount an RMR(R)/SRO(TM) on a MOS slide. Both optics ship with two long screws which will NOT work. You will need the two short screws in this kit.
Features:
Fits G17 Gen4 MOS G19 Gen4MOS G34 Gen4 MOS G35 Gen4 MOS G40 Gen4 MOS G41 Gen4 MOS and Springfield OSP.