What is a pre-shipment inspection, and what does AQL mean?

Once your order is finished, the factory asks for the balance. A pre-shipment inspection is how you find out what’s in the cartons before you pay it and before the goods leave the factory.

What is a pre-shipment inspection?

It’s a check of a finished order at the factory, done before it ships. An inspector picks units at random from the packed lot, checks them against your specification, counts the defects and writes a report with photos. The result is pass or fail against limits you agreed with the factory in advance.

Most inspections cover:

• Quantity: the number of cartons and units against the packing list.
• Appearance and workmanship: dents, scratches, welds, finish, loose parts.
• Function: the unit powers on, heats, cools, locks or dispenses as it should.
• Specification: dimensions, materials, voltage, plug type, colors and branding.
• Markings and labels: the certification mark, the rating plate and model number, and the country-of-origin marking.
• Packing: carton strength, crating, inserts and shipping marks.

You can book the inspection yourself with an independent inspection company, so the report comes to you. That’s the point of a third party inspection: someone who works for you does the counting.

What does AQL mean?

AQL stands for acceptance quality limit. The original US military standard called it the acceptable quality level and defined it as “the maximum percent defective (or the maximum number of defects per hundred units) that, for purposes of sampling inspection, can be considered satisfactory as a process average.”

So a limit of 2.5 tells the factory that a process running at up to 2.5 percent defective will pass most of the time. It isn’t permission to ship bad units. The same standard says the limit doesn’t give the supplier “the right to supply knowingly any defective unit of product.”

The sampling tables come from the US military standard MIL-STD-105. Its 1963 revision, 105D, was adopted as ANSI Z1.4 in 1971 and as ISO 2859 in 1974. According to NIST, the three standards keep being revised, “but the basic tables remain the same.” The current international version is ISO 2859-1, whose newest edition is dated 2026.

How does AQL sampling work?

This is acceptance sampling: you inspect part of the lot and decide whether to accept all of it. NIST describes it as “the middle of the road” between no inspection and 100 percent inspection. It answers one question, whether to accept this lot. It doesn’t measure the lot’s exact defect rate.

The steps, as NIST lists them:

1. Decide the acceptance quality limit.
2. Decide the inspection level.
3. Count the lot size.
4. Look up the sample size code letter.
5. Look up the sample size and the accept and reject numbers.
6. Start with normal inspection, and follow the switching rules on later lots.

General Inspection Level II is the default unless you specify otherwise. Level I takes smaller samples and Level III larger ones. Special levels S-1 to S-4 are for cases where only small samples are practical and you can accept a larger sampling risk.

The inspector picks the sample “at random without regard to their quality”, from cartons across the whole lot. If they find as many defects as the accept number or fewer, the lot passes. If they hit the reject number, it fails.

How to read an AQL table

Here’s an excerpt from the table for single sampling at normal inspection, General Inspection Level II, from MIL-STD-105D. The column headings are AQL values. Ac is the most defects you can accept, and Re is the number that fails the lot.

Lot size	Code letter	Sample size	1.0 (Ac / Re)	2.5 (Ac / Re)	4.0 (Ac / Re)
151 to 280	G	32	use the H plan	2 / 3	3 / 4
281 to 500	H	50	1 / 2	3 / 4	5 / 6
501 to 1,200	J	80	2 / 3	5 / 6	7 / 8
1,201 to 3,200	K	125	3 / 4	7 / 8	10 / 11
3,201 to 10,000	L	200	5 / 6	10 / 11	14 / 15

Here’s an example with made-up order numbers. You order 400 units, so the code letter is H and the inspector checks 50. You set 2.5 for major defects and 4.0 for minor ones. The lot passes on major defects with 3 or fewer and fails at 4. On minor defects, it passes with up to 5 and fails at 6. Each class is judged on its own, so the lot has to pass both.

Small lots work differently. In the table, some cells hold an arrow instead of numbers, which means you use the first plan the arrow points to. On a made-up order of 12 units at 2.5, the arrow leads to a sample of 5 with zero defects allowed. The standard also says that if the sample size equals or exceeds the lot size, you inspect every unit. On a short run of large equipment, checking every unit is often simpler than sampling.

Critical, major and minor defects

The standard sorts defects by how serious they are:

Class	What it means	Example on equipment
Critical	Likely to make the product hazardous or unsafe to use or maintain	Exposed live wiring, a missing ground, a sharp edge on a door
Major	Likely to cause failure or materially reduce usability	A compressor that won’t start, a door that won’t seal, the wrong voltage
Minor	Unlikely to affect use, or a small departure from the standard	A light scratch on a side panel, a crooked label

You can set a different limit for each class. Set the tightest limit for critical defects. The standard lets the buyer inspect every unit for critical defects and reject the lot “immediately, when a critical defect is found.” You can also reject any defective unit you find, even when the lot as a whole passes.

What goes on the inspection checklist?

The standard defines a defect as “any nonconformance of the unit of product with specified requirements.” So an inspector can only fail what your specification spells out. Write the checklist before production starts and send it to the factory with the order.

A useful checklist includes:

• The model numbers, quantities and carton count.
• Dimensions with tolerances, materials and finish.
• The electrical rating, voltage and plug type for US use.
• The certification marks that must appear on each unit. A UL or ETL listing covers the complete unit under its model number, and the testing lab itself inspects production at the factory. Our guide to UL, ETL and NSF marks explains what each mark means.
• The country-of-origin marking. Imported articles must show the English name of the country of origin, “legibly, indelibly, and permanently”, on the article or, where allowed, its container.
• Function tests the inspector should run, such as power on, temperature pull-down or door seals.
• Branding, labels, manuals and accessories in each carton.
• Packing and shipping marks.
• The AQL for critical, major and minor defects, and what happens if the lot fails.

Photos of an approved sample help too, since the inspector can compare each unit against what you signed off.

When should you inspect, and what if the lot fails?

Inspect once production is finished and the order is mostly packed, so the inspector can draw from the real shipping cartons. Book it before the balance is due. Once the balance is paid and the goods have sailed, you’ve given up your strongest bargaining position.

Agree the failure terms in your purchase contract. Options include sorting or reworking the whole lot followed by a reinspection, replacing the failed units, or holding shipment and payment until the lot passes. Settle who pays for a reinspection too. If you’re still choosing a factory, our guide on how to find and vet an overseas manufacturer covers the checks to run before you pay a deposit.

How Tally Wholesale inspects orders

Every order is inspected at the factory before it ships. We supply certified units only, and the listings for each model are named in your quote. A 50% deposit starts production, and the balance is due before the equipment ships.

If something still arrives damaged, defective or short, report it with photos within 7 days of delivery and we’ll replace or credit it, as set out in our shipping and returns policy. For custom builds on equipment orders, we run specs or paid samples first, with the sample cost credited to the production order. If you buy direct from a factory, our custom sourcing service can run this inspection for you. How it works covers each step from quote to delivery.

To get started, request a quote with the equipment, quantity and delivery ZIP code.