This is a Hi-Viz Sight known as the Magnetic, model M300.
HIVIZ(R) M-Series Narrow Magnetic Shotgun Sight. Fits shotguns with ribs from .218" to .328" (7/32" to 21/64") (5.5mm to 8.3mm). Includes Green and Red replaceable LitePipes in two diameters plus the unique HIVIZ two-toned LitePipes (green LitePipes with a red center).
Features:
Narrow fits ribs from .218 to .328
Green .135 green .175 red .135 and two tone .175
