Why does the used case market check start with wall thickness?

Answer: Thickness is the one item nobody can repair: below 2.0 mm the case is scrap, while an 18 RMB gasket and 26 RMB wheels are routine swaps, so 4 minutes remove most rejects.

How do I judge a gasket on the used case market?

Answer: Measure free height — 9.0 mm new, replace under 7.6 mm — then fold it 180° and look for 0.1 mm cracks. At 8.8% compression the lip no longer seals, and an 18 RMB strip beats any re-test.

Which parts are certainly due at 7 years?

Answer: Gasket, wheels, liner and valve diaphragm are due by design life, about 116 RMB in parts; the latch spring joins them at 30 N.

How long does the check take, and why sample 3 units?

Answer: 20 min per case: shell 4, gasket 3, hardware 5, wheels 3, liner 5. Three units expose a 0.15 mm thickness spread that one sample cannot show.

Is a 55% asking price fair on the used case market?

Answer: Only if the due parts were already replaced. A refurbished case at 649 RMB works; an untouched one lands at 841 RMB, 71% of new, and should be pushed to 45%, or 531 RMB.

Used Case Market: Five Checks

Quick answer: The used case market rewards 5 checks — shell, gasket, hardware, wheels, liner — in 20 min, with 2.0 mm wall and 0.4 mm hinge play as stop lines.

The Price Gap: Where 45–60% Comes From
Gasket: Measuring Compression Set
Hardware: Hinge Play and Latch Return
Wheels and Liner: The Two Quiet Items
The 20-Minute Order and the 35% Cap
FAQ

1. The Price Gap: Where 45–60% Comes From

One 520 mm × 420 mm × 210 mm case lists at 1,180 RMB new; a reseller asks 649 RMB, 55% of new. The 531 RMB gap looks like depreciation, but the shell carries little of it: an injection-moulded shell is rated past 10 years, and a 7-year-old shell kept out of sunlight still holds about 80% of its strength. The money sits in four items that wear and can be swapped.

Item	Look at	Measure	Line
Shell	Rim lip, corner ribs	5-point thickness, chalk depth	Under 2.0 mm, scrap
Gasket	Section height, lip	6 points, 180° bend	Set over 18%, replace
Hardware	Pin, bore, striker	Feeler, force gauge	Play over 0.4 mm, replace
Wheels	Tread, bearing, housing	Spin, push, measure	End play over 0.8 mm
Liner	Foam face, cut edges	10 s rub on paper	Chalk over 30%, replace

That is what the used case market check is for: 531 RMB split into five lives. Parts cost 152 RMB; 40 min of labour at 60 RMB/h adds 40, so 192 RMB in total. Pay 649 and spend 192, and the landed cost is 841 RMB, 71% of new — past the line where 55% stops being cheap.

The band: buy-in 20–25% of new, refurbishment 8–12%, storage and capital 10%, the rest margin. Under 45%, refurbishment was skipped. Over 60%, buy new.

2. Gasket: Measuring Compression Set

A gasket fails in height. A new strip stands 9.0 mm free in a 3.0 mm groove; the lid squeezes it to 6.75 mm, a 25% compression carrying about 80% of the sealing force. A 7-year-old strip usually measures 7.4 mm, or 8.8%, and the lip stops touching the rim.

Used case market inspection: a black case tilted open, grey foam with empty cutouts and two metal rods, two latches, one round valve cap

Six caliper points along the strip show a spread: past 0.3 mm, part of it has collapsed. Fold it 180° and look for 0.1 mm cracks — a hardened compound. Free height under 7.6 mm, or a crack at the fold, means replacement — 18 RMB and 15 min.

The groove hides a trap: a strip glued in place tears the 0.3 mm groove lip as it comes out, and the new strip will not seat. Lift one corner — glue residue and a frayed back mean non-factory repair, worth 100 RMB off. Gasket life is 3 to 4 years, so at 7 years it is due.

3. Hardware: Hinge Play and Latch Return

The pin is φ6 mm in a φ6.2 mm bore, a 0.1 mm fit when new. After 10,000 cycles a 7-year-old case measures 0.45 mm and the lid rocks 1.2 mm at 45°. Past 0.4 mm, replace the pin: 9 RMB each, both together.

Open the lid to 45°, push 30 N each way with a dial gauge on the corner, and divide by the lever ratio; without a gauge, a 0.4 mm feeler between pin and lug settles it.

Latch return comes next. A new latch opens at 55 N and snaps back within 2 s; a tired spring drops under 30 N and the striker still moves 0.5 mm after closing. A stepped striker costs 8% of compression and wastes the new gasket. Close both latches and listen for one sound.

An oval bore is the hard call: pull the pin 3 mm, read at right angles; over 0.4 mm difference means a new pin lasts six months and the lug goes.

4. Wheels and Liner: The Two Quiet Items

On a 100 mm wheel, end play is what gets missed. Push sideways: past 0.8 mm the race is pitted, and a sandy hiss means grit has reached the grease. At 1.5 mm of tread loss a 35 kg case pulls to one side. Wheels are 26 RMB each, so four come to 104 RMB.

Used case market bench test: a black open case on white, egg-crate lid foam, foam holding a screen unit with red sockets, red grip handle

The liner is waved through most often. PE foam at 30 kg/m³ that chalks more than 30% of white paper in 10 s is breaking down, and a 1 mm burr on cut edges sheds crumbs. A set costs 60 RMB and 10 min.

5. The 20-Minute Order and the 35% Cap

Work from the most expensive item down: shell 4 min with five thickness points, gasket 3, hardware 5, wheels 3, liner 5 — 20 min. The shell goes first because a scrap shell makes the other four checks pointless.

Item	Life	At 7 years	Cost
Gasket	3–4 years	Due	18 RMB
Wheels	4–5 years	Due, bearing audible	26 RMB each
Liner	5–6 years	Due, shedding	60 RMB
Latch spring	6 years	Borderline, 30 N	22 RMB per pair
Hinge pin	8 years	0.3–0.5 mm play	9 RMB each
Valve diaphragm	6 years	Due, 4 s return	12 RMB
Shell	Over 10 years	Read the chalk	Not replaced

Refurbishment is capped at 35% of new: 1,180 × 35% = 413 RMB. Parts of 152 plus 40 of labour are 192 RMB, 16.3%, leaving 221 RMB for teardown risk. So 649 plus 192 is 841 RMB, 71%: walk away. At 531 RMB the landed cost is 723 RMB, 61%: worth talking about.

Sample 3 units per batch: a 0.15 mm thickness spread or a 0.1 mm pin spread means mixed cavities, and the lot prices at the worst unit.

Item	Limit	Spread across 3	Meaning
Wall thickness	2.0 mm or more	0.15 mm	Mixed cavities
Hinge play	0.4 mm or less	0.10 mm	Uneven service
Gasket height	7.6 mm or more	0.30 mm	Different storage
Liner chalk	30% or less	15%	Water exposure

Conclusion

Run the five checks in one fixed order and the price question answers itself. Shell first, 4 min, five thickness points, and a lowest reading under 2.0 mm ends the inspection. Gasket next, 3 min, 7.6 mm free height and 0.1 mm fold crack. Hardware, 5 min, with 0.4 mm pin play and 35 N force written down. Wheels, 3 min, end play over 0.8 mm. Liner, 5 min, chalk on more than 30% of the paper. Add the 192 RMB of parts and labour to the asking price, divide by the new price, then act: under 70% is negotiable, over 70% is a pass. Hold refurbishment to 413 RMB, the 35% cap, because a case that needs more has a shell problem the other four checks cannot fix.

This article discusses container-side specifications and design implications only, and does not cover any handling, loading or use of the contents.