Holosun HSCQD1 Red Dot Sight QD Mount, Lower 1/3 Co-Witness. Manufactured from 6061 T6 aluminum, this T-1 optics interface Holosun red dot sight quick detach mount is perfect for quickly applying your Holosun optics system to the rail of any applicable firearm. This mount includes a spacer to achieve a lower 1/3 co-witness mount height with the Holosun 503 and 403 series of optics. (4) Installation screws and an allen wrench included.