Intermatic K4251 Stem and Swivel Mount Thermal Photocontrol, 120 V

The K4251 is a 120 VAC unit, 50/60 Hz. It is a single-voltage photocontrol, so it won't work on a 208-277 V branch circuit. If your fixture is fed at 120 V, this is the right one.

It mounts through a knockout with a 1/2"-14 NPSM threaded stem on a swivel arm. The swivel lets you aim the photocell away from the lamp and toward the north sky after the stem is through the hole. A washer gasket and locking nut come in the box, so you don't need to source sealing hardware separately.

Yes. The stem is 1/2"-14 NPSM, which is the standard trade size threaded stem used on wall packs, flood housings and pole-head knockouts. The body itself measures 4 in by 1.375 in by 1.375 in, so it takes up very little room alongside the fixture.

No. The K4251 has a built-in time delay that keeps a brief flash of light, like headlights or a neighboring fixture cycling, from switching the unit off. It only responds to a sustained change in ambient light level.

It's a thermal photocontrol: a mechanical bimetal switch driven by a cadmium sulfide photocell. The bimetal heats and cools to make and break the contacts, which is why it switches gradually rather than snapping instantly. That slow crossover is fine for incandescent and most HID loads, but it is a different behavior from an electronic photocontrol, which is generally what you want for LED and electronic-ballast drivers.

It's built for outdoor lighting control. The housing is high strength, UV resistant plastic in grey, so it won't chalk or go brittle from sun exposure the way untreated plastic does, and the included washer gasket seals the stem where it passes through the fixture knockout.

No. The washer gasket and locking nut ship with the photocontrol, so a knockout, a screwdriver and wire nuts finish the install.