Guide
How do you set up receiving inspection for machined and cast parts, and when can you skip lots?
Receiving inspection is the check a buyer runs on purchased parts when they arrive at the dock, before they are released to stock or the line: it confirms the shipment is the right part at the right revision, arrived undamaged, and conforms on the few characteristics that would hurt most if they were wrong. It is not a second final inspection, and a good plan gets smaller over time as the supplier earns it.
By Saola Manufacturing engineering team · Published · Updated
Most receiving plans for machined and cast parts fail in one of two directions. Either the dock measures everything on the drawing on every lot, which turns a receiving clerk into a bottleneck and still misses the one feature that matters, or it counts boxes and checks the packing list, which catches nothing. This guide is about the design of the plan itself: which checks belong at the dock, which characteristics deserve a gauge, how sampling and the supplier’s own records divide the work, and the rules for moving a part number to skip-lot and back again. The statistics of choosing a sample size are covered separately in the AQL sampling guide; here the sample plan is one input among several.
On this page
What should a receiving inspection check on machined and cast parts?
Check four layers in order: paperwork and identity, packaging and transit damage, visual and cosmetic condition, and then a short list of measured characteristics chosen by risk. The first three are fast and catch problems no gauge will; the fourth is where the gauges and the sampling plan go.
Paperwork and identity. Match the part number and drawing revision on the label, the packing list and the supplier’s inspection record against your purchase order. A wrong revision is one of the most expensive defects a dock can miss, because every part in the lot can be dimensionally perfect to the wrong drawing. Confirm the documents the order called for are present: a certificate of conformance, a lot dimensional record, material certification if specified, and a finish or salt-spray report if the order asks for one. Missing paperwork is a hold, not a pass with a note.
Packaging and transit. Ocean freight means humidity cycles, stacking loads and handling. Look for crushed cartons, loose parts rattling against each other, corrosion bloom on bare steel, and missing thread protectors or caps on sealing faces. Photograph damage before anything is unpacked; the carrier claim and the supplier conversation both depend on it.
Visual and cosmetic. Compare against the cosmetic standard named on the order, whether a boundary sample, a written specification or marked-up photos, rather than the inspector’s own taste. On machined parts look for burrs in cross-holes, chatter on sealing faces and missed operations such as an untapped hole. On castings look for cold shuts, flash, gate and overflow remnants left proud, and porosity opened up on machined faces. On finished parts look at coverage in recesses, coating in threads that were meant to be masked, and color or gloss against the sample.
Measured characteristics. Only the features whose failure would stop the line, leak, loosen or fail an assembly fit. Everything else is covered by the supplier’s process and records.
How do you build a receiving inspection plan for one part number?
Start from the drawing, mark each characteristic critical, major or minor by consequence, and assign each class a check method, a sampling plan and a skip-lot rule. Write it as a one-page plan per part number so the dock does the same thing every time.
The plan below is an example for a die-cast aluminum housing with machined bores and tapped holes, ordered in lots of about one thousand. It shows the pattern rather than numbers to copy: critical features get a zero-acceptance plan and never skip, functional fits get a normal attribute plan, and the long tail of dimensions is not measured at the dock at all because the supplier’s lot record covers it. The sample sizes come from the general inspection level II tables; the AQL guide explains how they are read and what risks they carry.
| Check | Class and method | Normal sample (pieces) | Reduced sample (pieces) | Skip-lot eligible |
|---|---|---|---|---|
| Part number, revision, documents | Hold point, every carton label | Every lot | Every lot | Never |
| Packaging and transit damage | Visual, every carton | All cartons | All cartons | Never |
| Sealing bore diameter | Critical, plug gauge, c = 0 (AQL 0.15 column) | 80 | 32 | No |
| Tapped holes, M6-6H | Major, go/no-go thread gauge, AQL 0.65 | 80 | 32 | Yes, after qualification |
| Mounting hole pattern | Major, check fixture, AQL 0.65 | 80 | 32 | Yes, after qualification |
| Cosmetic faces and finish | Minor, boundary sample, AQL 2.5 | 80 | 32 | Yes, after qualification |
| Remaining dimensions | Supplier lot record reviewed, not re-measured | 0 | 0 | Record review only |
Three choices in that plan are worth copying. First, document and revision checks are a hold point on every lot with no sampling and no skipping; they cost minutes and protect everything else. Second, the measuring method is named for each line, because a receiving inspector with calipers and a supplier with a plug gauge will often disagree on a bore. Third, the plan says explicitly which characteristics the dock does not measure. Leaving that unsaid is how receiving slowly grows into a full layout of every lot.
How many parts should the dock actually inspect?
Use a recognized sampling scheme for the measured characteristics and let the lot history move you between normal, tightened and reduced inspection. Inspect every part only for a critical feature when the supplier has no process control on it, and treat that as a temporary containment, not a plan.
The attribute schemes in ANSI/ASQ Z1.4 and ISO 2859-1 are built to be applied to a continuing series of lots with switching rules (ASQ, Z1.4 and Z1.9; ISO 2859-1:2026). Per MIL-STD-105E, the 1989 military standard from which Z1.4 and ISO 2859-1 descend, inspection tightens when two lots in any run of five or fewer consecutive lots are rejected on original inspection, returns to normal after five consecutive tightened lots are accepted, and may move to reduced inspection only when the preceding ten normal lots were all accepted, the total nonconforming found in their samples is within the limit number of Table VIII, production is at a steady rate, and reduced inspection is judged desirable. Any rejected lot on reduced inspection sends the part back to normal (MIL-STD-105E, paragraph 4.7). Those rules are the whole reason the plan gets cheaper: a dock that stays on normal inspection forever is paying for evidence it already has.
The switching rules only work if somebody keeps the lot log. Record, per part number, the lot number, the sample size, the count of nonconforming parts by characteristic, and the disposition. A spreadsheet is enough. Without it, nobody can say whether the part has earned reduced inspection, and the first rejection after a quiet year lands with no history to judge it against.
One common mistake deserves a mention: re-measuring everything the supplier already measured. If the supplier’s dimensional record for the lot shows the critical bore and your sample agrees with it, the record has been validated and can carry more weight next time. If your sample disagrees, that disagreement is the most valuable finding of the inspection, often a gauge or datum dispute rather than a bad lot, and it should go back to the supplier with both sets of numbers.
When can a part number move to skip-lot inspection?
Move a part number to skip-lot only after a run of consecutive accepted lots under normal inspection, with a stable design, process and supplier location, and drop it straight back to lot-by-lot inspection on the first rejection or any change. Critical characteristics and the paperwork check never skip.
Skip-lot sampling inspects only a fraction of submitted lots and accepts the rest without inspection. The NIST handbook describes the mechanics: start with lot-by-lot inspection to a reference plan, switch to inspecting only a fraction of the lots once a set number of consecutive lots has been accepted, and return to normal inspection when a lot is rejected; it adds that the method should only be used when it has been demonstrated that the quality of the submitted product is very good (NIST/SEMATECH e-Handbook, 6.2.7). ISO 2859-3 formalizes the same idea and frames it as a way to reduce inspection effort for a supplier who has a satisfactory quality system and effective controls, with the lots to be inspected chosen at random (ISO 2859-3:2005). The 2026 third edition of ISO 2859-1 also brings skip-lot procedures into the main standard, so name the document and edition your order relies on.
Two details make or break it. The selection must be random, decided at receiving, and not predictable by the supplier; a fixed “every fourth lot” pattern invites the good lots to be the inspected ones. And the qualification and disqualification rules must be written down before the first lot skips, so nobody argues about them after a problem. A practical qualification and disqualification list:
- Qualify after a written run of consecutive accepted lots at normal inspection, with no open corrective action on the part number and the supplier’s lot records agreeing with your samples.
- Disqualify on any lot rejection, any customer complaint traced to the part, a drawing revision, a new or repaired die or fixture, a material or finish change, a move to a different machine line or plant, or a long gap between shipments.
- Requalify from normal inspection again, not from where the part left off.
The change triggers matter more on cast parts than machined ones. A repaired or replacement die can move a parting line, shift porosity into a machined face or change shrink on a critical boss, and none of that shows in the history of the old tool. Ask the supplier to tell you about tooling changes in writing, and treat the first lot after one like a partial first article; the first article inspection guide covers what that report should contain.
What changes when the parts are die castings rather than bar-stock machined parts?
Castings add defects that live inside the part or appear only after machining, so the dock cannot see them with a gauge. The plan has to lean on the supplier’s process tests and on a few targeted checks rather than on more dimensions.
Internal porosity, for example, is controlled at the supplier by process, sectioning or radiography, not at a receiving bench. If porosity matters for strength or sealing, put the requirement on the drawing and the order, such as a radiographic grade per ASTM E505 on named zones, and ask for the record; the ASTM E505 guide explains how to write that callout. If the housing must hold pressure, the leak test belongs at the supplier, on every part or a defined sample, with the result in the lot record; the leak testing guide covers methods and limits. At receiving, the useful casting checks are visual: opened porosity on machined sealing faces, cracks at bosses and ribs, and gate or flash remnants that interfere with assembly.
Threads in cast aluminum deserve their own line in the plan. A tapped hole that breaks into a pore gauges fine and still leaks or strips, so gauge the thread with go/no-go gauges per the thread gauging guide and also look into the hole for exposed porosity, which the gauge alone will not reveal.
What should the purchase order and RFQ say so the receiving inspection works?
State the inspection the supplier performs, the records each lot must carry, and the characteristics you will check on receipt, all before the first order. A supplier who knows what the dock will measure, and how, can gauge the same way.
Typical clauses that make receiving fast and disputes rare:
- “Each lot shall ship with a dimensional inspection record listing measured values for the characteristics marked as control dimensions on drawing 1234-567 Rev C, with lot number and measuring method.”
- “Critical characteristics marked on the drawing are accepted on zero nonconforming in the sample. Thread acceptance is by go/no-go gauges per the thread standard named on the drawing.”
- “Cosmetic acceptance per the approved boundary sample dated at sample approval; faces not marked cosmetic are functional only.”
- “Supplier shall notify the buyer in writing before shipping product made after any change of drawing revision, tooling, material, finish, process or location.”
- “Each carton shall be labeled with part number, revision, quantity and lot number.”
Federal contracts show the same structure in plain terms: the government has the right to inspect and test supplies at all places and times, including the period of manufacture, and the right either to reject or to require correction of nonconforming supplies (FAR 52.246-2). Commercial orders rarely need that much text, but they do need the rejection path written down: who pays for screening, whether the supplier sorts at your dock or the lot returns, and how a replacement lot is inspected. The RFQ guide shows where these clauses sit in the package.
What does Saola send with a lot that a receiving inspection can use?
Every production lot ships with a dimensional inspection record of sample measurements against your drawing, and every new part starts with a first-article inspection report. Material certification, salt-spray results and a RoHS declaration are available on request.
That record is what your receiving plan can review instead of re-measuring. When a drawing marks a dimension as a process-capability control point, the plant treats it as one of the values watched through the run and checks it more often than the rest of the print, so marking your critical receiving characteristics as control dimensions lines up both inspections on the same features. Cosmetic acceptance runs to the standard you supply, a boundary sample, written specification or marked-up photos, and the plant asks for one before production if none is supplied. Thread fit on turned parts is checked with go/no-go gauges before a lot ships, as described on the CNC turning page, and machined castings are covered on the CNC milling page. ISO 9001 certification is in progress and not yet held, and no third-party quality audit report exists yet, so specify the records your receiving plan relies on in the order. The full list is on the quality and inspection page, and a drawing with your receiving plan attached can go straight to a quote request.
Frequently asked
Is receiving inspection the same as incoming inspection?
Yes, the two names are used for the same activity: checking purchased material on arrival before it is accepted into stock. Some plants reserve “receiving” for the count, paperwork and damage check and “incoming” for the measured inspection; if your procedures make that split, say which one a part number’s plan covers.
Can a third-party inspection at origin replace receiving inspection?
It can replace most of the measured inspection, because a problem found before shipment is far cheaper to fix than one found after an ocean crossing. It cannot replace the paperwork, labeling and transit damage checks, which only exist once the goods arrive.
Should skip-lot apply to the whole part or to individual characteristics?
Apply it per characteristic class within a part number. A stable cosmetic and hole-pattern history can earn skip-lot while a sealing bore stays on every lot, which is usually where the real risk sits.
What should happen to a lot that fails receiving inspection?
Quarantine it, record the nonconformance with measured values and photos, and send both to the supplier before deciding between return, sort at your site or a use-as-is deviation. Move the part number back to normal or tightened inspection under the switching rules and ask for a corrective action on the cause, not just a replacement lot.
Sources
- NIST/SEMATECH e-Handbook of Statistical Methods, 6.2.7, What is skip lot sampling?, NIST, 2012, accessed October 2026
- ISO 2859-3:2005, Sampling procedures for inspection by attributes — Part 3: Skip-lot sampling procedures, ISO, 2005
- ISO 2859-1:2026, Sampling procedures for inspection by attributes — Part 1, ISO, 2026
- ANSI/ASQ Z1.4 and Z1.9 overview, ASQ, accessed October 2026
- MIL-STD-105E, Sampling Procedures and Tables for Inspection by Attributes, U.S. Department of Defense, 1989
- FAR 52.246-2, Inspection of Supplies — Fixed-Price, U.S. General Services Administration, accessed October 2026