What do the markings on my container mean?

The four letters and seven digits are a name and a number

That big code down the side is the container's identity in the worldwide freight system, and it reads in two halves. The first three letters are an owner code issued to whoever put the box into service, normally a shipping line or a leasing outfit that rents steel to shippers. The fourth letter is nearly always U. That one character says the unit is a box in its own right, not a chassis under it and not a swap body lifted off a truck frame.

Then come six digits of serial number and one final digit set slightly apart, usually in a box of its own. That last one is a check digit, a piece of arithmetic run against everything before it so a clerk keying the number into a terminal system finds out immediately if a digit got fumbled. The same code is repeated on the doors, the far end and often the roof, because the box gets read from a crane cab as often as from the ground.

Here is what it does not tell you. The owner code names the fleet that ran the container, not the factory that built it, and a box can change hands several times without anybody repainting the side. Treat it as a name tag, not a history.

The plate by the door is the only marking carrying a date

Look at the left door and you will find a small metal plate riveted or welded flat to the steel. That is the CSC plate, named for the international safety convention that requires it, and it is the closest thing a container has to a birth certificate. Stamped or etched into it you get the build date, the manufacturer, the approval reference, and the structural ratings the box was certified to when it left the line.

Alongside it you will often see a separate decal for a continuous examination program, which is how a fleet keeps a box legal for ocean service without hauling it in for a scheduled survey every few years. Those dates lapse once a container retires into the resale market, and that is normal. A lapsed examination date has nothing to do with whether the steel is sound.

If the plate is gone, the container can still be a perfectly good storage box, but the paper trail behind it is gone with it. Ask why it went missing. On our own rows the plate is one of the things we look for before a unit is offered, and it is on the walk-around in our used container inspection checklist.

Tare, payload and max gross: read your own door

The block of numbers near the doors is three ratings in pounds and kilograms. Tare is what the empty container weighs by itself. Payload, sometimes stencilled as net or max cargo, is the most freight it was certified to carry. Max gross is the two added together, the heaviest the whole loaded box was rated to be when a crane picked it up.

We do not publish weight figures for our inventory, and we are not going to invent one for yours, because these move from unit to unit depending on the build and the year. As a rough order of magnitude an empty 20 ft typically weighs 4,800 to 5,100 pounds, with an empty 40 ft landing near 8,200 to 8,800. Your own door carries the real number for your unit, painted next to the CSC plate. Read that, not a chart.

One more thing worth knowing: max gross is a shipping rating. It describes what the frame and corner castings were certified to handle hanging off a crane, which is a far harder job than sitting still on blocks. For a container holding mowers and feed on level ground, the number is trivia.

The short code that tells you the size and the shape

Somewhere near the ID you will usually find a four character code such as 22G1, 42G1 or 45G1. It is compact and it is useful. The first character encodes length, the second encodes height and width, and the last two say what type of container it is. G1 covers general purpose dry boxes, which is nearly everything we handle.

So 22G1 is a standard 20 ft, 42G1 is a standard 40 ft at the same 8 feet 6 inches of exterior height, and 45G1 is a 40 ft high-cube standing a foot taller at 9 feet 6 inches. If you are trying to work out what you are looking at across a row from twenty feet away, that code settles it faster than counting corrugations.

High-cube units carry one more marking you should know: a yellow and black diagonal striped band near the top of the doors, warning anybody hauling it that the box is over standard height. That stripe is the cheapest bridge clearance reminder ever painted, and it is worth respecting.

What the markings will never tell you

This is the part that matters most. Nothing painted on the outside of a container reports the condition of the floor, whether the roof has ponded and gone thin, whether the door gaskets still compress, or whether rough handling has twisted the frame so the doors will not line up. A box with a crisp code and a clean CSC plate can still have a soft spot in the plywood.

• The markings say what the box was rated to do, not what shape it is in today.
• They do not record cargo history, so a chemical smell inside still has to be found by standing in there and breathing.
• They do not report repairs, patches or a repaint done in a depot yard.
• They cannot tell you whether the doors seal, which only a hand on the locking bars settles.

Which is the whole reason we keep the yard in Woodlawn and the sales lot in Wytheville open to buyers Monday through Friday. Read the plate, then walk around the box.

Painting over them is your call, with one caution

Plenty of people paint a container once it is set, either to knock down the shipping line colors or to satisfy a neighbor. Nothing stops you from rolling right over the ID code, and for a box that is never leaving your property it costs you nothing.

Work around the CSC plate, though. If you ever sell the unit on, nothing else on the box tells the next owner what year it was built or what it was rated to carry, and rolling it into a smooth grey rectangle quietly costs you at resale. Mask it, cut in around it, and let it keep doing its job.