B-Line Eaton series imperial cable tray and ladder, 4" Height, 9.78" Length, 12" Width, 12" and 9" Tray widths, Series 2-5 left reducer, Aluminum

It's a transition fitting that steps a 12 inch wide tray down to a 9 inch wide tray, with the reduction taken on the left side so the right side rail stays in line. Aluminum construction, 4 inch loading depth, and 9.78 inches long in the direction of the run. Use it where the cable fill drops off partway along a run and you want to carry the smaller tray onward without breaking the alignment of one rail.

The offset side. A left reducer takes the width reduction on the left rail as you look along the run, keeping the right rail straight; a right reducer does the opposite. There is also a straight (center) reducer that splits the reduction evenly across both rails. The 4A-12-LR09 is the left version, 12 inch down to 9 inch. Pick based on which rail your conduit drops, supports or wall clearance are referenced to, and remember that looking at the run from the other end reverses what you call left.

Aluminum. It weighs 2.2 pounds, so the fitting itself adds almost nothing to the hanger load, and aluminum is the usual choice where you want corrosion resistance without galvanizing or paint. Keep the material consistent through the run: mixing aluminum fittings into steel tray introduces dissimilar metal contact at the splice plates, and the bolt patterns are not intended to be crossed between material families.

Model 4A-12-LR09 from Eaton's B-Line series. The number reads out as 4 inch height, aluminum, 12 inch nominal width, left reducer to 9 inch. Splice plates and hardware to join it to the adjoining straight sections are ordered separately to match your tray series.

It is CE marked. That is the certification held on record for this aluminum reducer; no other listing or rating is claimed for it.