The D4A0009N is a limit switch head from Omron's D4A series, with a top-mounted plunger actuator and maintained action — meaning the contacts stay in the switched state after the plunger is released, until mechanically reset. The IP67 rating means the head is sealed against dust and temporary immersion in water, so it holds up in washdown areas or outdoor installations where moisture and debris are present. The stainless steel arm and plunger handle corrosive environments and physical impact better than plastic or zinc alternatives, and the 17.65 N operating force gives a positive snap action that resists nuisance tripping from vibration.
Mounts on the D4A switch body — the head is the actuator portion, so you need the corresponding switch base to complete the assembly. The fixed arm and 0.06 in arm depth mean the plunger position is non-adjustable; layout the cam or striker accordingly. The NEMA enclosure ratings cover 1, 2, 3, 4X, 5, 6P, 12, 13 — that's indoor and outdoor, with corrosion resistance (4X) and submersion (6P). For a hot-strip mill or furnace-adjacent installation, the -40 °F to 212 °F operating range takes the radiant heat better than commercial-temp limit switches.