This is a Hi-Viz Sight known as the Magnetic, model M400.
HIVIZ(R) M-Series Wide Magnetic Shotgun Sight. Fits shotguns with ribs from .328" to .437" (21/64" to 7/16") (8.3mm to 11.1mm). Includes Green and Red replaceable LitePipes in two diameters plus the unique HIVIZ two-toned LitePipes (green LitePipes with a red center).
Features:
Wide fits ribs from .328 to .437
Green .135 green .175 red .135 and two tone .175
