Container twist lock dimensions and corner castings

Container corner casting dimensions (ISO 1161)

Each fitting is cast for its position: the right-hand fittings are mirror images of the left-hand ones, and the bottom ones are the same as the top ones except for the hole in their end face. A fitting is marked with its maker, its heat number and a certification mark. A 45 ft box has eight more fittings at the 40 ft positions, so that it can sit on 40 ft boxes and trailers (45 ft container).

What are the corners of a shipping container called?

Corner castings, or corner fittings, in the words of ISO 1161: the eight cast blocks at the ends of the corner posts and of the top and bottom rails. Cranes lift the box by the top ones, twist locks hold it by the bottom ones, and stacked boxes rest on each other through them.

Container twist lock dimensions

A twist lock’s head must pass through the 124 × 63.5 mm top hole of a corner casting before it turns, so it is a little smaller: about 104 × 56 mm, by one encyclopedia’s figure. ISO 3874, the standard on handling and securing containers, sets the dimensions and strength of twist locks in an annex we have not read: before you buy, ask the seller for the drawing of the lock and check that it fits your box or your trailer. A cast semi-automatic twist lock weighs about 8 kg on one Indian supplier’s listing.

Twist lock positions on a 20 ft and 40 ft trailer: distances between corner castings

These are the distances at which a trailer, a rail wagon or a ship carries its twist locks, which is why a 20 ft box fits any 20 ft trailer. An Indian maker’s 40 ft skeletal trailer has twelve twist locks, set to carry one 40 ft box, two 20 ft boxes, or one 20 ft box in the centre. The diagonals measure how square the box is: a used box whose diagonals differ by more than the standard allows has been bent, and its twist locks may not engage.

Types of container twist locks

• Manual twist lock: turned by a handle to lock and to unlock.
• Semi-automatic twist lock (SAT): locks by itself when the upper box is set down, and is unlocked by hand.
• Fully automatic twist lock (FAT): locks and unlocks without anyone at the box.
• Midlock: used where two 20 ft boxes stand in a 40 ft bay on a ship.
• Stacking cone: a locating piece between two boxes that keeps them in line but does not lock them.
• Trailer and wagon twist locks: fitted to the chassis at the corner positions.
• Weld-on twist lock sockets: steel bases welded to a deck, a trailer or a foundation plate, into which a twist lock or a box fits.

Most of these terms are defined in ISO 3874. The IMO’s code on cargo securing asks ships to use as few types as possible, with locks that lock positively and cannot drop out of the fitting, and prefers semi-automatic or automatic ones.

How strong is a twist lock?

A classification society’s guide to container securing gear sets a minimum breaking load of 500 kN for a twist lock, about 51 tonnes force, and a safe working load of 299 kN; a maker’s fully automatic lock is rated to break at 500 kN in tension, 420 kN in shear and 2,000 kN in compression. One trailer-parts maker in India tests its trailer twist lock for a box of 35 tonnes gross on four locks. Classification societies certify securing gear on request; for a box on your land, ask the seller for the lock’s rating and any certificate.

Which twist lock for which use, and how many?

• On a ship: semi-automatic or automatic locks between the boxes, which is the shipping line’s business.
• On a trailer: the trailer’s own locks at the four bottom corners of each box; check that all four are turned before the truck moves.
• Two boxes stacked on a site: four twist locks or stacking cones between them, one at each corner, so that the upper box cannot slide off.
• A box fixed to the ground: weld-on sockets or plates on the foundation, with twist locks, are one way to anchor it, four per box. Singapore’s Building and Construction Authority, in a 2023 circular, asks for a converted container to be anchored to its foundation so that wind and other loads pass to the ground, leaves the method to the engineer, and forbids cutting the corner fittings. We found no Indian rule on anchoring a container; on cyclone coasts, ask a structural engineer, who will work to India’s wind code, IS 875 part 3. Site preparation and unloading explains the supports under the corners.

The doors of a container take a padlock through their handles, and some boxes have a welded lock box: see how a container door works.

Container twist lock price in India

Asia Containers does not sell twist locks. As a guide, three Indian suppliers’ sites, read on 26 October 2026, asked:

• about ₹1,300 to ₹1,350 a piece for a manual twist lock, in stainless steel or chrome-plated mild steel, for a minimum of 20 pieces, and about ₹600 for a mild steel trailer lock, for 40 pieces;
• about ₹750 to ₹2,500 a piece for iron twist locks with a lever or a screw, from 1 to 100 pieces;
• ₹4,300 a piece for a cast semi-automatic twist lock, for 10 pieces, and ₹2,450 for a reconditioned manual one, for 50.

These are asking prices, mostly marked approximate, without GST stated, and not checked with the sellers. Most sellers ask for 10 to 50 pieces at a time, while one box needs four.

Checking the corner castings of a used container

The corner castings carry the whole box when it is lifted and stacked. On a used box, look at all eight: no cracks around the holes, no welded repairs on the casting itself, holes neither bent nor worn larger, and no deep rust where the casting meets the posts and rails. Try a twist lock in a bottom fitting if you will stack or truck the box. How to inspect a used container gives the other checks.