Why order three case sampling sizes instead of one?

Answer: Coverage. One medium case reaches 46%, three tiers reach 82%, and 2660 yuan over 14 days beats three rounds costing 480 yuan and 22 days more.

Can the small tier stand in for a whole-unit test?

Answer: No. Its 130 mm internal height will not take a 150 mm module, and wall thickness does not scale, so it serves die trials and hand-held use.

Is 175 mm internal height enough on the medium tier?

Answer: It takes a 400 × 300 × 150 mm module plus 25 mm of liner, but not a 200 mm upright instrument, which goes to the 230 mm large tier.

Do all three samples need a pressure test?

Answer: Medium and large do, at -0.3 kPa with decay under 0.5 kPa in 60 seconds; the small tier needs a 1 m, 30-minute immersion.

Can 14 days be cut to 10?

Answer: Two days, by running die and body in parallel. Beyond that the order splits in two and the second 5-day die run stays.

Case Sampling Sizes: Choosing Sizes for Sampling

Quick answer: Case sampling sizes start at three, not one: a single medium case covers 46% of field scenarios, while small, medium and large samples reach 82% for 2660 yuan in 14 days and verify liner, seal and stacking in one round.

Start With Three Cases, Not One
Small: 380 × 300 × 150 mm for Hand-Held Work
Medium: 480 × 380 × 200 mm for the Main Verification
Large: 620 × 480 × 260 mm for Whole Units and Stacking
Verification, Cost and Lead Time
FAQ

1. Start With Three Cases, Not One

The first order usually holds one case: the largest unit is measured, 30 mm is added, and one box ships. Back it comes with small parts rattling, and only the third round shows the right combination.

Case sampling sizes are a question of coverage: one medium case serves hand-held work, spares and whole instruments at 46%, a small case lifts it to 71% and a large one to 82%. The remaining 18% is long rods and oversize items, which belong to custom tooling.

Plan	Samples	Case and liner cost	Lead time	Coverage
Medium only	1	880 yuan	12 days	46%
Medium plus small	2	1620 yuan	12 days	71%
Small, medium, large	3	2660 yuan	14 days	82%
Three separate rounds	3	3140 yuan	36 days	82%

Samples from one lot compare; three months apart, even wall thickness drifts. The 480 yuan saved by splitting the order is freight, and the 22 days lost are benches rebooked.

2. Small: 380 × 300 × 150 mm for Hand-Held Work

The small tier is 380 × 300 × 150 mm outside, 330 × 250 × 130 mm inside, 10.7 L usable and 1.6 kg empty. It matches hand-held inspection: a torque wrench, two probes and a 200 g meter leave 30% for foam.

Treating it as a scale model is the usual error: a 3 mm wall carries 1.6 times the empty-weight share it does on the medium case, and the drop curve differs.

EVA dies are priced by area, 380 yuan at 330 × 250 mm against 720 yuan at 560 × 420 mm, so cutting the small one twice costs 760 yuan. It also takes the first drop for the medium, at 1.6 kg empty plus 4 kg of ballast from 1.2 m.

Stacking runs 3 high, so 4.2 kg loaded puts 8.4 kg on the bottom case, tested at 25 kg for 24 hours against a 2 mm limit.

3. Medium: 480 × 380 × 200 mm for the Main Verification

The medium tier is 480 × 380 × 200 mm outside, 425 × 325 × 175 mm inside, 24.2 L and 2.8 kg empty. It is the only one that carries a whole-unit test alone: a 400 × 300 × 150 mm module fits the 425 × 325 mm floor with 25 mm for liner.

Tier	Outside	Inside	Usable volume	Empty weight	Sample price
Small	380 × 300 × 150 mm	330 × 250 × 130 mm	10.7 L	1.6 kg	480 yuan
Medium	480 × 380 × 200 mm	425 × 325 × 175 mm	24.2 L	2.8 kg	620 yuan
Large	620 × 480 × 260 mm	560 × 420 × 230 mm	54.1 L	4.5 kg	780 yuan

Liner follows 30% compression: EVA at 45 kg/m³ returns 96% after 25%, so 25 mm on the floor and 15 mm on the walls are the floor of the range; thinner bottoms out in a 1 m drop.

This is the first tier worth a pressure test: -0.3 kPa, decay held to 0.5 kPa in 60 seconds.

Stacking at 12 kg loaded puts 24 kg on the bottom case, tested at 72 kg for 24 hours, or 3.9 kPa over the 480 × 380 mm top; past 2 mm the ribs span over 300 mm.

Internal height is the limit: 175 mm will not take a 200 mm upright instrument, so that goes to the 230 mm large tier, which means a new mould anyway.

4. Large: 620 × 480 × 260 mm for Whole Units and Stacking

The large tier is 620 × 480 × 260 mm outside, 560 × 420 × 230 mm inside, 54.1 L and 4.5 kg empty. It does two jobs: whole units and stacking.

Case sampling sizes: broad machine table with a black mat in a moulding hall, control cabinet on the left, hazard stripes on the frame, two workers behind

54.1 L looks generous until an 18 kg unit and 18% of foam leave 44 L, which two coils of cable finish; plan at 80% utilisation.

Stacking must be measured here: 3 high at 18 kg puts 36 kg on the bottom case, tested at 108 kg for 24 hours, or 3.6 kPa over the 0.30 m² top.

It is also the only pallet sample: four per layer and two layers make 1.1 m on a 1200 × 1000 mm pallet, half a 2.4 m trailer.

5. Verification, Cost and Lead Time

Three samples from one batch mean one pass of tests on the same lot.

Test	Method	Limit	Tiers	Time
Liner compression	25% for 24 hours	Recovery ≥95%	All three	26 hours
Pressure	-0.3 kPa held 60 seconds	Decay ≤0.5 kPa	Medium, large	1 hour
Immersion	1 m for 30 minutes	No trace inside	All three	1 hour
Stacking	3 times load for 24 hours	Top face ≤2 mm	Medium, large	25 hours

Case sampling sizes: long showroom shelf running back to the wall, grey black and green cases on pale wood boards, timber floor, cartons in the corner

Units cost 480, 620 and 780 yuan, so 1880 yuan for three; liners at 260 yuan each add 780 yuan for 2660 yuan total. The body leaves an existing mould in 7 days and the liner die takes 5 in parallel, so three cases are ready on day 12, the large tier adding 2 days.

Order the tests so each leaves the sample usable: compression first, since load changes liner thickness; pressure and immersion while the gasket is new; stacking last, because residual distortion would spoil a pressure reading. Number the samples on arrival, small 1 to large 3.

Conclusion

Put the three tiers on one matrix and case sampling sizes stop being a guess: small at 380 × 300 × 150 mm takes 38% of hand-held work, medium at 480 × 380 × 200 mm takes 27% of spares and cabling, large at 620 × 480 × 260 mm takes 17% of whole units and stacking, and together they reach 82%. Each tier owns one scenario, one limit and one price; the remaining 18% belongs to custom tooling.

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