B-Line Eaton series imperial cable tray and ladder, 6" Height, 27" Length, 24" Width, 24" and 9" Tray widths, Series 2-5 horizontal reducing tee, Alum

The 6A-24-09-HT12 horizontal reducing tee joins a 24 inch wide run to a 9 inch wide branch. That is the whole point of a reducing tee: the main run stays at 24 inches and the tee drops the branch down to 9 inches, so you do not need a separate reducer fitting at the junction.

Lay out for 27 inches of length and 24 inches of width on the fitting itself, with a 12 inch inside bend radius on the turns. The radius matters more than the footprint on a cable job - 12 inches is what keeps the conductors inside their minimum bend radius as they turn into the branch. Check your cable's bend radius against that 12 inches before you commit.

Aluminum. It has to match the tray it is spliced into - mixing aluminum fittings into a steel run creates a dissimilar metal joint and breaks the continuity assumptions of the system. Aluminum also keeps the piece light: the tee weighs 14.1 lb, so one person can set it on the trapeze before bolting up.

It carries a UL Classified marking. For an inspector on a cable tray installation, that is the mark they look for on the fitting as well as the straight sections.

A straight reducer narrows a run in line - 24 inches down to 9 inches, same direction. This 6A-24-09-HT12 is a horizontal tee, so it takes a 24 inch run and breaks a 9 inch branch off it in the horizontal plane while the 24 inch run continues through. If you are branching a smaller feeder off a main run in a flat ceiling plane, the tee is the piece. If the main run itself is getting narrower past that point, you want a reducer instead.