B-Line Eaton series imperial cable tray and ladder - Length 19.5 in, Width 9 in, Height 4 in - Aluminum

It is an expanding tee: the run and branch are not the same width. The fitting is built for 9 inch and 18 inch tray widths, so it takes you from one width to the other at the branch instead of forcing a separate reducer. If both legs of your intersection are the same width, you need a straight horizontal tee, not this expanding version.

Aluminum. That is what you want when the tray run is aluminum ladder, both for galvanic compatibility and for the weight: the fitting comes in at 11.84 lb, light enough for one electrician to set on trapeze hangers overhead. If your existing run is steel tray, match the steel version instead of mixing metals.

The fitting measures 19.5 in length/depth, 9 in width, and 4 in height. The 4 inch height is the side rail depth, which needs to clear whatever is above and below the run, and the 19.5 inch dimension is what you have to allow for the fitting body itself before the next tray section starts. Lay it out against your hanger spacing before you cut tray to length.

The 4A-09-18-HT12 tee is UL Classified. Inspectors on commercial and institutional jobs routinely ask for that on tray fittings, and it is stated for this part. Anything beyond the classification itself, such as a specific ampacity figure, should be taken from the manufacturer's published tables for the series.

No. A horizontal expanding tee turns the run in the horizontal plane only, all three legs staying at the same elevation. To change elevation you need vertical inside or outside elbows, or a vertical tee, on the same 12 inch radius as this fitting so the cable bending radius stays consistent through the system.

Order it as Eaton B-Line 4A-09-18-HT12. That single number carries the aluminum material, the 9 by 18 inch expanding tee configuration, and the 12 inch radius, so there are no separate options to specify.