Thomas & Betts 321-TB Armored Cable/Flexible Metal Conduit Fittings, 100 Pack

The 321-TB takes cable or flex with an outside diameter from 0.470 to 0.660 inch, which is the 3/8 inch nominal trade size. If your armored cable or flexible metal conduit measures outside that range, it is the wrong fitting.

No. The 321-TB is a 3/8 inch trade size fitting and threads into the matching 1/2 inch knockout that size uses. For a 3/8 inch cable going into a 3/4 inch knockout, the Arlington Industries 407AST SNAP2IT is built for that combination.

The Arlington Industries 407AST is a SNAP2IT MC cable connector sized for a 3/4 inch knockout while accepting 3/8 inch cable, in a 100 pack. The Thomas & Betts 321-TB is a 3/8 inch nominal fitting whose throat is long enough to install in cast housing knockouts, so match the connector to the knockout diameter in the box or enclosure you are landing on.

Yes, that is its purpose: it connects and effectively bonds armored cable or flexible metal conduit to a box or enclosure. It is steel with an electro zinc plated finish, so the metal path is continuous from the cable armor through the fitting to the enclosure.

The 321-TB is a threaded, screw-type 90 degree fitting with an external thread, so it is secured to the box with a locknut and the cable is clamped. The Arlington Industries 380ST SNAP2IT is a 3/8 inch snap-in design that pushes into the knockout without a locknut, which is faster on open-wall work. Both are sold 100 to a pack. Choose the 321-TB where you need the 90 degree turn at the box or a long throat for a cast housing.

Not in the same geometry. The 321-TB is a 90 degree connection, so the armored cable or flexible metal conduit leaves the enclosure at a right angle, which helps in tight stud bays and against blocking. The Arlington 380ST is a SNAP2IT MC/AC cable connector in 3/8 inch for 100 count packaging, and it is the choice when a straight entry into the knockout is acceptable.

The Thomas & Betts 321-TB is steel with an electro zinc plated finish and carries UL E23018 and CSA 2884. If the submittal also calls for a snap-in style body in the same 3/8 inch cable size, the Arlington Industries 380ST is a SNAP2IT series MC/AC connector in 3/8 inch, 100 per pack, and the Arlington 407AST is the SNAP2IT version for a 3/4 inch knockout with 3/8 inch cable.

The Thomas & Betts 321-TB is rated for a wire size range of 0.470 to 0.660 inch at a 3/8 inch nominal size. The Arlington 380ST and 407AST are both described as 3/8 inch MC/AC cable connectors in the SNAP2IT series, so all three address 3/8 inch trade size cable; confirm your cable OD falls inside the 0.470 to 0.660 inch window if you go with the 321-TB.

Sold 100 to the outer carton, packed as two inner boxes of 50. Carton weight is 12.5 lbs per 100.

The steel body is zinc coated (electro zinc plated) for surface protection, which handles general indoor and unfinished interior work. It is a bonding fitting, not a liquidtight one, so for wet locations or where water can run on the connection you want a liquidtight flex connector instead.