B-Line Eaton series imperial cable tray and ladder, 4" Height, 30" Length, 30" Width, 30" and 36" Tray widths, Series 2-5 horizontal reducing tee, Alu

It is made for exactly that pairing. The 4A-30-36-HT12 tee mates 30 inch and 36 inch wide tray, so one leg lands on 30 inch tray and the other on 36 inch. Side rail height is 4 inches, so the tray it connects to has to be 4 inch rail as well. If both of your runs are the same width, this is the wrong fitting, you want a straight horizontal tee instead of a reducing one.

The 12 inch radius is the inside bend radius the conductors follow through the fitting. That number is what you check against the minimum bending radius of the cable you are pulling, since the fitting, not the cable, sets the tightest curve in the run. The 4A-30-36-HT12 is the 12 inch radius version of the Series 2-5 horizontal reducing tee. If your cable spec calls for a larger bend radius, a 12 inch radius fitting will not satisfy it.

Aluminum. The 4A-30-36-HT12 reducing tee is an aluminum fitting, which is the usual choice where weight on the supports matters or where a steel tray would be a corrosion problem. Match it to aluminum tray so you are not creating a dissimilar metal joint at the splice.

The 4A-30-36-HT12 is listed at 4 in height, 30 in length/depth and 30 in width, with a 12 in radius. Use those numbers to check clearance above ceilings and around structure before the branch gets set, since a reducing tee needs more room at the intersection than a straight section does.

Order Eaton B-Line 4A-30-36-HT12. That designation breaks down to the 4 inch rail height, the 30 and 36 inch tray widths it joins, the horizontal tee fitting, and the 12 inch radius. Splice plates and hardware for tying it into the adjacent tray sections are ordered separately.

23.03 lb. That is the fitting alone, before cable fill, and it is worth adding into your support spacing calculation because a reducing tee concentrates load at a branch point where you typically want a hanger on each leg.