B-Line Eaton series imperial cable tray and ladder - Length 33 in, Width 12 in, Height 4 in

The Eaton B-Line 4A-12-18-HT24 is a 12 inch wide tray section with a 4 inch side rail height, and it measures 33 inches in length. Those three numbers decide whether it drops into your run: the 12 inch width sets your cable fill area, the 4 inch rail depth sets how deep the loading channel is, and the 33 inch length is what you get per piece, so plan your support spacing and splice points around that rather than around a full 10 or 12 foot stick.

The 4A-12-18-HT24 is sold as the tray section itself. Splice plates, hold-down clamps, hangers, trapeze channel, anchors, covers, and any fittings such as elbows, tees, or reducers are separate items you order to suit the run. Budget those in when you count sections, because a 33 inch piece means a splice joint at every 33 inches.

You get 12 inches of usable width between the rails' nominal designation and a 4 inch rail height to load into, so fill is limited by the NEC fill rules for your conductor type rather than by the tray. If your cable bundle needs more than that, step up to a wider section in the same series instead of stacking above the rail, since cable stacked proud of a 4 inch rail cannot be held by covers or hold-downs.

A 33 inch section suits exactly that: a short jog between fittings, a chase or wall penetration, a transition piece, or making up length at the end of a run where a full stick would have to be field cut. For long horizontal runs you are better off ordering full length sections of the same series so you are not adding a splice every 33 inches.