B-Line 4A-30-18-HT24 Eaton series imperial cable tray and ladder - Length 42 in, Width 30 in, Height 4 in - Aluminum

It joins a 30 inch wide tray run to an 18 inch wide branch. That is what makes it a reducing tee rather than a straight tee: the run and the branch are different widths, so you do not need a separate reducer fitting between them. Overall the fitting measures 42 in length, 30 in width and 4 in height.

24 inch radius. That matters because cable manufacturers set a minimum bending radius for the cable being pulled, and the fitting's radius has to equal or exceed it. If your cable spec calls for a tighter radius, a 24 inch fitting is still fine; if it calls for something larger, this tee is not the one.

Aluminum. It weighs 26.9 lb, which is a two-hand lift for one installer on a lift or scaffold. Aluminum is the usual pick where the run is outdoors, in a corrosive area, or where you want to keep dead load on the supports down. If your existing run is galvanized steel tray, match the material rather than mixing at the joint.

Use the reducing tee when the branch leaves the main run at a different width, which is exactly what the 4A-30-18-HT24 does going from 30 inch to 18 inch. One fitting, one set of splices, and the reduction happens inside the turn. A straight tee plus a reducer means two fittings, extra splice plates and more support points, and it eats more straight run length. Go that route only when you need the reduction at a point away from the intersection.

Order Eaton B-Line 4A-30-18-HT24. The number reads out the build: 4 inch loading depth, aluminum, 30 inch run, 18 inch branch, horizontal tee, 24 inch radius. Distributors cross-referencing can also use UPC 781011084219.

Allow 42 inches of length and 30 inches of width for the fitting body, with a 24 inch turn radius on the branch. Lay that out before you set your hangers, because the support spacing either side of a tee is driven by where the fitting ends, not by where the straight tray stops.