Guide
What should a pre-shipment inspection check on machined and cast parts before they leave an overseas plant?
A pre-shipment inspection is the last look at a finished, packed lot while it is still at the supplier’s site: it is your chance to prove the parts match the drawing revision, the purchase order and the agreed quality requirements while a bad lot can still be sorted, reworked or remade. For machined and cast parts it has to measure the characteristics that matter against the drawing, not only count cartons and look at the surface, or the problem it exists to solve, a nonconforming lot discovered after an ocean crossing, comes straight back.
By Saola Manufacturing engineering team · Published · Updated
Most pre-shipment inspection checklists published online were written for consumer goods: count the cartons, open a random sample, look for scratches, check the labels and the shipping marks. That is a useful start for a housing or a bracket, but it misses the reasons machined and cast parts actually get rejected at the customer’s dock: a bore that is out of position, a thread that will not accept the gauge, the wrong alloy, porosity opened by machining, a finish that is the right color but the wrong thickness. This guide turns the generic checklist into an inspection brief a buyer can hand to the supplier or to a third-party inspector, explains what an inspector at origin cannot verify, and gives the purchase-order wording that makes the inspection binding.
On this page
Why do bad lots of machined and cast parts still get past a pre-shipment inspection?
Because the inspection usually checks what is easy to see at a factory dock, not what the drawing actually controls. Cartons, labels and cosmetics pass while position tolerances, thread fit, material and coating thickness go unmeasured.
The symptom is familiar to anyone who imports parts. A lot is released with a clean inspection report, spends weeks at sea, and then fails on the assembly line or at receiving inspection: screws will not start in tapped holes, a sealing face leaks, a mating part will not seat, or the plating rusts in the warehouse. The report was not necessarily dishonest. It answered the questions it was asked, and nobody asked the right ones.
In the WTO Agreement on Preshipment Inspection, the term refers to checks that some importing governments, mostly in developing countries, require on the price, quantity, quality and customs classification of goods before export (International Trade Administration, WTO PSI trade guide). In commercial sourcing the buyer commissions the inspection instead, and the scope is whatever the buyer writes down. That is the point to hold on to: a pre-shipment inspection is only as good as its brief.
What causes a defective lot to be found only after ocean freight?
The usual causes are an inspection brief with no drawing characteristics in it, an inspector without the gauges or skills for the part, sampling that ignores critical features, and requirements that cannot be checked at origin at all.
- No characteristic list. The inspector was given a part number and a quantity, not a ballooned drawing with the characteristics to measure. Without balloons, each inspector picks the dimensions that are easy to reach with a caliper.
- Wrong tools for the tolerance. A caliper cannot verify a true-position callout or a tight bore. Datum-referenced features under ASME Y14.5 need a fixture, a height gauge setup, a vision system or a CMM, and a general inspector rarely brings any of these.
- Sampling that treats every defect alike. An AQL plan written once for the whole part lets a critical defect slip through at the same rate as a cosmetic one. Critical characteristics need their own plan, often accept-on-zero, as covered in the AQL sampling guide.
- Requirements that only a lab can prove. Alloy grade, heat treatment, internal porosity and corrosion performance cannot be read off a part at the dock, so they must be covered by records generated earlier in production.
- Revision drift. The plant built to an older drawing revision, and the inspector checked to the same old revision because that is what was on site.
- The inspected lot is not the shipped lot. Cartons are topped up, swapped or re-packed after the inspector leaves, so the report describes parts that never went into the container. Mark or seal the sampled cartons and ask for the carton count and marks in the report.
- Packing that damages good parts. Unprotected threads, parts loose in a carton and bare steel without corrosion protection turn a conforming lot into a damaged one in transit.
What should a pre-shipment inspection brief for machined and cast parts contain?
The brief should name the drawing and revision, list each characteristic to measure with its method and sample size, state the cosmetic standard, and define the quantity, marking and packing checks. Anything not written in the brief will not be inspected.
Build the brief from the ballooned drawing, and mark which balloons are critical, major and minor so the inspector knows where zero defects is the only answer. The critical characteristics guide explains how to flag them on the print. For appearance, refer to a physical standard such as a golden sample and limit samples rather than words like “no visible defects”. Sample sizes for attribute checks can be taken from the general inspection level tables of ISO 2859-1:2026 or ANSI/ASQ Z1.4, with the acceptable quality limit chosen by defect class.
| Brief item | What the inspector checks | Method and basis |
|---|---|---|
| Identity and paperwork | Part number, drawing revision, PO quantity, lot or heat number on labels and packing list | Compare against the PO and the current drawing revision supplied with the brief |
| Critical characteristics | Each critical balloon: positions, bores, sealing faces, thread fit | Fixture, gauge, vision system or CMM; accept-on-zero sampling or the plant’s full measurement record reviewed |
| Major characteristics | Functional dimensions not marked critical | Hand gauges or height gauge; general inspection level II sample, tighter AQL |
| Threads | Every threaded feature on the sampled parts | Go/no-go thread plug or ring gauges of the class on the drawing |
| Cosmetic and casting surface | Burrs, chatter, cold shuts, flash, gate remnants, porosity opened by machining | Golden sample and limit samples under stated lighting |
| Finish | Coverage, masking of threads and contact faces, color and gloss, coating thickness | Visual against limit samples; eddy-current gauge for anodize on aluminum (ASTM B244-09(2021)); magnetic gauge for paint or powder coat on steel (ASTM D7091-22); plating thickness by the method the plating specification names |
| Quantity and packing | Count per carton, thread protectors, separation, corrosion protection, carton marking | Count and open cartons from the sampled set; photograph the packed lot |
| Records review | First-article report, lot dimensional record, material and finish records called for by the PO | Check that each record exists, matches the lot and shows conforming results |
Which requirements can an inspector at origin not verify on the spot?
Material composition and condition, heat treatment, internal casting porosity, corrosion performance and anything requiring a destructive test cannot be proven at a final inspection. They have to be covered by records made during production and reviewed by the inspector.
A handheld XRF analyzer can sort alloys and a portable hardness tester can confirm that a heat-treated part is roughly in range, but neither replaces a mill or lab certificate. Internal porosity in a die casting is found by radiography, sectioning or leak testing, not by looking at the outside, so a casting with a pressure-tight requirement needs a production leak test record; the leak testing guide covers the methods. A salt-spray result takes days to generate in a lab, so it belongs to the finish qualification, not the final check.
Measurement capability is the other limit. A general inspection agency usually sends an inspector with calipers, micrometers, thread gauges and a camera. For datum-referenced features the better arrangement is for the inspector to witness the plant measuring a sample on its own CMM or vision system, check that the instruments have current calibration records traceable as described in the calibration certificate guide, and then re-measure a few parts personally with simpler gauges as a cross-check. When you hire an agency, ask whether it is accredited to ISO/IEC 17020, the conformity assessment standard for inspection bodies, and whether the inspector assigned to your part can read GD&T.
| Requirement | Verifiable at a pre-shipment inspection? | What to rely on instead |
|---|---|---|
| Simple sizes, thread fit, visual and packing | Yes, directly | Inspector’s own gauges and samples |
| True position, profile, runout to datums | Partly: witness and cross-check | Plant CMM or vision record, witnessed, with calibration status shown |
| Coating thickness | Yes, with a portable gauge of the right type | Finisher’s thickness record for the batch |
| Alloy grade | Screening only (handheld XRF) | Material certificate traceable to the lot |
| Heat treatment and hardness depth | Surface hardness spot check only | Heat treat record and hardness report |
| Internal porosity, pressure tightness | No | Production leak test record or radiographic report |
| Corrosion performance of the finish | No | Salt-spray or other qualification test report for the finish |
What should happen when a pre-shipment inspection finds a nonconformance?
Hold the lot, decide by defect class whether to sort, rework, remake or accept under a written deviation, and re-inspect before release. The decision must be yours in writing, never the plant’s or the inspector’s by default.
- Critical defect found. Reject the lot as sampled. Ask for full sorting of that characteristic with a record of every part, then a re-inspection by the same inspector.
- Major defect above the acceptance number. Sort or rework, with the rework method approved by you. Rework on a machined feature, such as re-tapping or re-boring, can change other characteristics, so re-measure the related balloons.
- Cosmetic or minor defect. Decide against the limit samples. If you accept, issue a written deviation naming the lot and quantity, so it does not become the new standard.
- Missing records. Treat as a hold, not a pass with a note. A lot without its material or finish record is a lot you cannot prove.
- Packing defect. Repack before release and photograph the corrected cartons.
Most disputes after a failed inspection come from a vague report, so set the reporting rules before the inspector arrives:
- Book the inspection when the lot is complete and packed, not partly made, so the count and the carton marks in the report are the ones that ship.
- Send the same brief and drawing revision to the plant and the inspector, and have the plant confirm which gauge or instrument it will use for each critical balloon.
- Require measured values, not OK/NG, for every critical and major balloon, tied to a part or carton number, so a borderline reading is visible.
- Ask for photos of the gauge on the feature for threads and bores, and of the sampled cartons with their marks.
- Seal or mark the sampled cartons and, for a first shipment, consider a container-loading check so the inspected cartons are the ones loaded.
Whatever the decision, ask for a root-cause and corrective-action report so the same defect is not caught again on the next lot; the 8D report guide shows the structure. Finding the defect at origin is the cheap outcome; the expensive outcome is finding it after the parts have been shipped, cleared and installed.
What should the drawing, RFQ and purchase order say so the inspection has teeth?
The purchase order should make release for shipment conditional on a passed inspection to a named brief, state who performs it, and list the records that must ship with the lot. The RFQ should say the same thing so the supplier prices it.
Example clause, to adapt with your own counsel:
“Goods shall not be released for shipment until a pre-shipment inspection to inspection brief [document number, revision] against drawing [number, revision] has been passed and the report accepted in writing by the buyer. The inspection may be performed by the buyer or by an inspection body nominated by the buyer. Critical characteristics marked on the drawing are accept-on-zero. Each lot shall be accompanied by a dimensional inspection record for the ballooned characteristics, a certificate of conformance, and the material and finish records listed in the brief. Acceptance at origin does not waive the buyer’s right to reject nonconforming goods on receipt.”
On the drawing, keep the balloons and the critical-characteristic flags, and name the finish by specification rather than by color alone. In the RFQ, attach the brief and say whether you, a third party or the supplier’s own quality staff will inspect, because witnessed measurement time and the re-inspection of a sorted lot have a cost. Keep the last sentence of the clause in any version: a pre-shipment inspection reduces the chance of a bad lot arriving, but your receiving inspection still has to check paperwork, transit damage and the characteristics nobody could see at origin. The certificate of conformance guide covers what that document should state.
Who does what before parts ship on a Saola order?
Machined parts are made and measured at our lead CNC plant in Vietnam, and casting, stamping and finishing are done at partner plants we manage. Every quote names the production site and country of origin, which tells you where an inspection at origin would take place.
Parts from CNC milling and CNC turning are made at our lead CNC partner plant, T.K Viet Nam Precision Company Limited, in operation since 2017, where measuring equipment includes a 2D vision measuring machine, a height gauge and a hardness tester, and thread fit is checked with go/no-go gauges. Die casting, stamping and surface finishing go to partner plants we manage, which are not necessarily in Vietnam; the quote states where each operation runs and the resulting origin.
Every new part starts with a first-article inspection report against your drawing, and every production lot ships with a dimensional inspection record of sample measurements, which is the record a pre-shipment inspector can review and cross-check. Material certification, salt-spray results and a RoHS declaration are available on request, so list the ones your brief relies on in the order. ISO 9001 certification is in progress, not held. If you plan a pre-shipment inspection by your own staff or an inspection body, attach the brief to the RFQ so it can be planned before the order is placed. The documents themselves are listed on the quality and inspection page, and a drawing with its brief can go straight to a quote request.
Frequently asked
Is a pre-shipment inspection the same as a source inspection?
They overlap. Source inspection is the broader term for any buyer inspection at the supplier’s site, including in-process checks during the run. A pre-shipment inspection is the source inspection done on the finished, packed lot just before release.
Can a pre-shipment inspection replace receiving inspection?
It can replace most of the measuring, but not the checks that only exist after transit: transit damage, corrosion picked up at sea, mixed or missing cartons, and the paperwork that arrives with the goods. Keep a reduced receiving inspection.
Should the inspection be done during production or only at the end?
For a new part or a new supplier, add a check early in the run, after the first article is approved. Finding a drifting characteristic while the run is still on the machine is far cheaper than sorting a finished lot.
Who should write the inspection brief, the buyer or the supplier?
The buyer owns it, because the brief defines what acceptable means. The supplier can propose methods and gauges, and should confirm in writing that it can measure every characteristic listed before the order is placed.
Does a passed pre-shipment inspection mean the buyer has accepted the goods?
Only if the contract says so. Write into the purchase order that acceptance at origin does not waive the right to reject nonconforming goods on receipt, especially for defects that could not be detected at the inspection.
Sources
- Trade Guide: WTO Preshipment Inspection Agreement, International Trade Administration, U.S. Department of Commerce, accessed October 2026
- Agreement on Preshipment Inspection, World Trade Organization, 1994
- ISO/IEC 17020:2026, Conformity assessment: Requirements for bodies performing inspection (publication notice), NATA, 2026
- ISO 2859-1:2026, Sampling procedures for inspection by attributes, Part 1: Sampling schemes indexed by acceptance quality limit (AQL) for lot-by-lot inspection, ISO, 2026 (third edition, replaces the 1999 edition)
- ANSI/ASQ Z1.4-2003 (R2018) and Z1.9-2003 (R2018) overview, ASQ, accessed October 2026
- ASME Y14.5-2018 (R2024), Dimensioning and Tolerancing, ASME, 2018, reaffirmed 2024
- ASTM B244-09(2021), Measurement of Thickness of Anodic Coatings on Aluminum and of Other Nonconductive Coatings on Nonmagnetic Basis Metals with Eddy-Current Instruments, ASTM International, 2021
- ASTM D7091-22, Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals, ASTM International, 2022