B-Line Eaton series imperial cable tray and ladder, 4" Height, 19.5625" Length, 9" Width, Series 2-5 horizontal bend, Aluminum, 90° Angle, 12" Radius

That is exactly the size it is built for. The 4A-09-90HB12 is a Series 2-5 horizontal bend with a 9 inch inside width and 4 inch side rail height, in aluminum, so it splices into a 9 inch wide by 4 inch deep aluminum tray run. Match the tray width and rail height exactly; a bend sized for a different width will not line up at the splice plates.

Allow 19-9/16 inches of length for the fitting itself, measured 19.5625 inches, plus whatever clearance your hangers need at each end. On a 12 inch radius 90 degree turn that keeps the corner tight, which is the reason to pick this radius when you are working around structure or duct.

Aluminum is the material here, and it is chosen for weight and corrosion resistance. This bend weighs 7.184 lb, light enough for one person to set and hold while splicing overhead, and aluminum holds up in damp or mildly corrosive areas without galvanizing. Where you need higher load capacity or a lower material cost, a steel tray system is the alternative, but do not mix aluminum and steel in the same run without matching the fittings to the tray.

Horizontal bend means the tray turns left or right while staying at the same elevation. This one makes a 90 degree flat turn on a 12 inch radius. If you need the run to climb or drop, that is a vertical inside or outside bend, not this fitting.

Order Eaton B-Line part 4A-09-90HB12. The number decodes as 4 inch rail, aluminum, 09 for 9 inch width, 90 degree horizontal bend, 12 inch radius, which is a quick way to confirm you have the right fitting against a drawing.

The 4A-09-90HB12 is supplied as the bend section itself. Splice plates, hold-down clamps, and hanger or trapeze supports are ordered separately, and you will need a splice connection at each end of the fitting plus support within the spacing your tray run calls for.