Is a used flight case worth buying?

Answer: Yes when all five checks pass: moisture under 12%, extrusion above 1.8 mm, ovality under 0.5 mm, pin above 4.6 mm, foam back within 8 seconds.

How do I spot water in the core quickly?

Answer: Three signs: a meter reading above 16%, pale rings within 20 mm of the corner screws, and a dull tap over more than 30 mm × 30 mm.

Can a thinned extrusion still be used?

Answer: Down to 1.8 mm from 2 mm, and it survives two drops. Below 1.6 mm the 30×30 mm tube keeps 51% of its bending stiffness.

Does the foam always need replacing?

Answer: Only when it fails the press test. A 2 mm crater means set above 15%, and 90 CNY beats recutting compartments.

What duty cycle suits a used box?

Answer: Up to ten trips a year. Over 40 trips in four years the used box costs 16.5 CNY a trip against 35 CNY new.

Used Flight Case: Five Structural Checks

Quick answer: A used flight case is worth buying when five measurements pass: board moisture below 12%, extrusion wall above 1.8 mm, rivet hole ovality under 0.5 mm, hinge pin thicker than 4.6 mm, and foam rebounding within 8 seconds of a 5-second press. Pass all five and a 480 CNY box still has three years left.

Board First: 9 mm Against 12 mm
Extrusion and Corner Caps: The Rivet Hole Test
Latches and Hinges: Preload with a Feeler Gauge
Foam: Compression Set and Rebound
Wheels, Handle and Hardware: Wear Limits
The Money: 480 Against 1,400 CNY
FAQ

1. Board First: 9 mm Against 12 mm

Check the board before the hardware. A flight case body is 9 mm birch plywood, 13 plies at about 0.7 mm each, with a 12 mm base for forklift point loads. Second-hand boards fail two ways — water and delamination — and a 30 CNY pin meter reads both in 20 seconds.

Twelve percent is the line. Below 12% the board is recoverable; 12% to 16% needs seven days upright at 25 °C and 50% RH before a second reading; above 16% the glue has begun to hydrolyse and the case gains 1.2 kg of water weight. A dull knuckle tap usually marks a patch over 30 mm × 30 mm.

Board	9 mm birch ply	12 mm birch ply	9 mm PP honeycomb
Build	13 plies	17 plies	Honeycomb core, two skins
Area density, kg/m²	6.3	8.4	4.1
Bending stiffness, relative	1.0	2.4	0.7
After water	Edge swell 1.5 mm	Edge swell 1.2 mm	No uptake, skins debond
Repair	Epoxy and dowel	Epoxy and dowel	Replace the panel

One hidden defect is common: a pale ring within 20 mm of the corner-cap screws, where alkali bloom has already halved pull-out strength.

2. Extrusion and Corner Caps: The Rivet Hole Test

The frame is 30×30 mm aluminium tube, 2 mm wall when new, fixed with 4.8 mm blind rivets at 75 mm centres. What gets missed is ovality: after two rebuilds a 4.8 mm hole measures 5.2 mm and the rivet turns in place.

Used flight case on a steel bench: tan rotomoulded body, two black rubber latches, folding handle, white scuffing on the corner bumpers, shelving behind

Pull one rivet and try a 5 mm plug gauge. Under 0.2 mm of play passes; 0.2 to 0.5 mm needs 6 mm rivets with a backing washer; past 0.5 mm the hole needs a patch plate.

Corner caps are 2 mm stamped aluminium: check for weld cracks over 10 mm, a gap above 1 mm at the extrusion, and four rivets present. Lose one and the cap lifts 3 mm in a drop, taking the extrusion run with it.

3. Latches and Hinges: Preload with a Feeler Gauge

A butterfly latch is rated at 200 N of preload, which fingers cannot judge but a 0.3 mm feeler gauge can. Push the blade between tongue and seat: no entry means intact preload; 0.3 mm means clamping has fallen to about 120 N and the lid will chatter; 0.5 mm means it is finished.

Hinges are simpler — read the pin. A 5 mm pin is replaced at 4.6 mm, because 0.4 mm of clearance lets the lid shift 2 mm side to side as it drops. A re-welded leaf is a walk-away: the heat-affected zone anneals 1.5 mm sheet to 60% of its strength.

The part everyone forgets is the 1 mm plastic spacer under the latch seat. Without it the latch travels 1.5 mm further and no preload closes the gap.

4. Foam: Compression Set and Rebound

The foam is 45 kg/m³ EVA cut into compartments. Age shows in rebound, not colour. Press a thumb flat for 5 seconds and release: full thickness back within 8 seconds passes; a 2 mm crater after 8 seconds means compression set above 15%.

Used flight case opened in a warehouse: tan body, grey foam in the lid with cut marks, base divided into a dozen cells, shelving behind

A replacement runs 90 CNY for a 1200×600 mm cavity in three layers, 15% to 19% of a used box price — a cost buyers routinely leave out. Press the four corners, under the handle and the centre of the base, whatever the listing says.

A 3 mm gap between foam and wall means the box took a side squeeze. Measure the diagonals: a difference over 4 mm means the body is out of square.

5. Wheels, Handle and Hardware: Wear Limits

Wheel diameter 75 mm; replace at 2 mm of tread loss, all four together, 15 CNY each.
Wheel bearing play 0.4 mm; visible rocking means replacement before it chews the floor.
Handle wobble under 3 mm is fine; past 5 mm the inner bush is through.
Latch spring free length 18 mm; below 15 mm it no longer returns the tongue.

All four take five minutes with a tape and a caliper. Hardware is the only part replaceable item by item, so its limits sit wider: wheels, handle and latches are consumables; plywood and extrusion are not.

6. The Money: 480 Against 1,400 CNY

Item	New flight case	Used flight case
Purchase, CNY	1,400	480–650
Refurbishment, CNY	0	90–180
Remaining life	8 years	3–5 years
Annual amortisation, CNY	175	120–160
Single repair, CNY	20 (rivets)	45 (patch and rivets)

On a 1200×600×600 mm cavity, a new box at 1,400 CNY over 8 years amortises at 175 CNY a year; a used one at 480 CNY plus 180 CNY of refurbishment over 4 years lands at 165 CNY. The saving is in optionality: a six-month project writes off six years of depreciation at once, and a used box still resells for 200 CNY.

Past 900 CNY after refurbishment the arithmetic flips: another 300 CNY reaches 85% of a new price, with eight years and a warranty attached. A refurbished unit listed above 950 CNY deserves a new quote first.

Conclusion

Five rulers decide a used flight case: 12% moisture, 1.8 mm wall, 0.5 mm ovality, 4.6 mm pin, 8-second rebound — all readable on site in 20 minutes with a meter, feeler gauge, caliper and tape. The price advantage needs a short project and five passes; past 900 CNY of refurbishment, price a new box.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.