B-Line Eaton series imperial cable tray and ladder, 6" Height, 24" Length, 18" Width, 18" and 9" Tray widths, Series 2-5 horizontal reducing tee, Alum

The 6A-18-09-HT12 is a Series 2-5 horizontal reducing tee that ties an 18 inch wide tray to a 9 inch wide branch, so it both branches and reduces in one fitting. Overall it measures 18 inches wide by 24 inches long with a 6 inch side rail height. If your branch run is the same width as the main run, a reducing tee is the wrong fitting, you want a straight horizontal tee instead.

Aluminum. That keeps the weight down, 13.77 lb for this fitting, and suits outdoor, damp, and corrosive environments where a painted steel tray would need coating maintenance. Aluminum tray also needs a separate equipment grounding conductor or bonding jumper treatment per your engineer's detail, since mixing aluminum fittings into a steel run is not a like for like substitution.

No. The reduction is built into the fitting, so the 18 inch main run and the 9 inch branch land directly on the tee with no additional reducer section between them. You will still need the splice plates and hardware appropriate to the Series 2-5 aluminum tray at each of the three connection points, since those are ordered separately from the fitting.

Horizontal. The 6A-18-09-HT12 branches the run flat, in the plane of the tray, so it handles a side takeoff on a level run. Changes in elevation, up over a beam or down into a panel, call for a vertical inside or outside bend instead, not this fitting.

13.77 lb for the fitting itself. Add that to your cable fill when you space trapeze hangers, and remember a tee concentrates load at the branch point, so most installers hang a support close to each side of the fitting rather than relying on the adjoining straight sections.

It is CE marked. If your submittal or facility standard calls out other listings, confirm those against the manufacturer's published documentation for the Series 2-5 aluminum line.