Steel City XC 290 3/8 INCH CONN,90DEG,AC/FLEX,DC,CLMP

The XC 290 takes a 1/2 inch knockout. It is a 3/8 inch trade size connector, so the cable side handles 3/8 inch armored cable or flexible metal conduit while the threaded hub and locknut land in a standard 1/2 inch box opening. That pairing is the usual one for 3/8 inch AC/MC work, so it drops into a standard device box or panel knockout without a reducing washer.

Both, as long as they are 3/8 inch trade size. It is catalogued as an armored cable and flexible metal conduit fitting, so the same clamp body serves 3/8 inch AC (BX) whips and 3/8 inch flex runs. It will not take 1/2 inch flex, which needs the next size up.

That is exactly what the XC 290 is for. The 90 degree body turns the cable right at the box, so you are not forcing a bend radius in a stud bay or behind a panel where there is no room to run the whistle straight in. If you have the clearance for a straight approach, a straight 3/8 inch clamp connector is cheaper and quicker to land; the 90 is the one you reach for against a ceiling deck, a corner, or a shallow box.

It is a clamp type. The clamp screw tightens down on the armor, which is what lets one fitting hold both AC (BX) and flexible metal conduit in the 3/8 inch range instead of being cut for one product only. Practical upshot for an electrician: you land the cable, snug the clamp, and the fitting grips the spiral without needing a separate anti-short bushing to do the mechanical work.

Zinc die cast body. That is a dry location interior fitting for AC and flexible metal conduit, not a liquidtight or wet location fitting. If the run is exposed to weather, washdown, or standing moisture, specify a liquidtight flexible metal conduit connector with a sealing gland instead of this clamp type.

Country of origin on the XC 290 is India. Worth knowing if you are bidding public work with domestic sourcing language in the spec, since that clause will govern whether this fitting can be submitted.