Quality Documentation for a Spare Part or Tooling: What to Ask For and When
A five-piece spare part does not need a PPAP, but it cannot arrive with only an invoice either. This guide covers which documents to request depending on what you buy (dimensional report, material certificate, heat treatment certificate, FAI) and why they must be requested before quoting.
The spare part arrives, receiving logs it, maintenance installs it and the line restarts. Three weeks later it fails, and quality asks the obvious: what material was it? What hardness did it have? Did anyone measure the bearing seat diameter? Nobody knows, because the part came with an invoice and a packing slip. It is not that the supplier made a bad part; it is that nobody asked for the evidence, and evidence that is not requested is not produced.
The opposite extreme also exists: asking for the full series production package for a five-piece maintenance order. That does not raise quality; it only pushes the delivery date and the price. This guide is for the plant buyer or quality engineer who has to release a spare part or a tooling order: which documents to ask for depending on what you are buying, what each one must contain, and why they have to be requested before quoting.
In Summary
- PPAP is for approving series production, not for releasing a 1–10 piece spare part. For that there is a shorter package proportional to the risk.
- The typical package for a spare part or tooling is: dimensional report, material certificate and, where applicable, heat treatment or coating certificate. FAI only when the industry or the part justifies it.
- A dimensional report without measured values is not a report: it must identify each dimension against the drawing and state what was measured, with what, and the result.
- Documents are requested at quoting, because some cannot be produced afterwards and because their cost has to be in the price.
- At Radii, spare parts and tooling from tooling and MRO for plants ship with inspection and a dimensional report, and the documentation you need is defined in the quote.
1. Why a spare part does not need PPAP (and when it does)
PPAP exists for one specific question: can this supplier produce this part in series, meeting the drawing, repeatably? That is why it includes capability studies, a control plan, failure mode analysis and parts from a representative run. All of that is covered in the three quality pillars for a Tier 1 supplier, which is the production version.
A maintenance spare part or a tooling order asks a different question: does this part, the one being delivered to me, meet the drawing and is it the right material? There is no series to prove and no process capability to measure on five parts. What you need is evidence about those parts.
When a spare part can call for PPAP:
- When it is a service part for a series automotive product (the spare the OEM sells for a vehicle, not the spare for a machine in your plant). There, PPAP applies according to the customer's requirements, within AIAG's quality core tools.
- When the "spare part" is actually going to be bought recurrently in volume. At that point it stops being a spare and becomes a production part, and the package changes.
If neither applies, asking for PPAP means asking for documents that do not answer your question.
2. The possible documents and what each one proves
| Document | What it proves | When to request it |
|---|---|---|
| Dimensional report | That the delivered part was measured against the drawing and conforms | Whenever there are functional dimensions |
| Material certificate | What material it is, which heat it comes from and its properties | Whenever material matters (almost always for steel) |
| Heat treatment certificate | That the specified treatment was done and what hardness resulted | When the drawing calls for hardening, tempering, carburizing, nitriding |
| Coating or finish certificate | Coating type, thickness, standard | When the drawing calls for anodizing, black oxide, zinc, chrome |
| FAI (first article inspection) | That the first part meets every characteristic on the drawing, documented one by one | Aerospace, or tooling that will be reproduced |
| Certificate of conformance | Supplier's declaration that the part meets the order | Supplement only; never a substitute for the above |
The rule behind all of it: each document answers a different question. The dimensional report says nothing about material; the material certificate says nothing about dimensions; and the certificate of conformance proves nothing on its own, because it is a declaration, not a measurement.
3. What to ask for depending on what you buy
| What you buy | Reasonable package | What is excessive |
|---|---|---|
| Non-critical spare (guard, bracket, plate without fits) | Report of main dimensions, material certificate | Full report of every dimension |
| Functional spare (shaft, bushing, bearing seat, part with a fit) | Dimensional report of critical dimensions, material certificate with heat number, heat treatment certificate if applicable | PPAP |
| Tooling, fixture or jig | Full dimensional report, material certificate, heat treatment certificate for hardened parts | Capability studies |
| Gage or inspection part | Full dimensional report with instrument uncertainty, heat treatment certificate | — (here the report is the product) |
| Part that will be reproduced several times | FAI or full report of the first piece, which becomes the reference | Repeating the full report on every lot |
| Series automotive production part | PPAP at the level the customer requires | — |
| Aerospace part | FAI per AS9102, full traceability | — |
Two criteria for borderline cases:
- What happens if this part fails? If it stops a line or damages another machine, raise the package. If it is swapped in ten minutes with no consequences, lower it.
- Will you buy it again? If so, invest in a full report on the first one; the next ones are compared against it.
4. The dimensional report: what it must include
It is the most requested document and the one most often delivered poorly. A useful dimensional report includes:
- Drawing number and revision. If the drawing changed revision and the report does not say so, you do not know what it was measured against.
- Each dimension identified. Ideally a ballooned drawing: each dimension with a number, and the report with the same numbers. That way it can be reviewed without interpretation.
- Nominal, tolerance and measured value for each dimension, not just "OK."
- Instrument used (CMM, micrometer, caliper, height gage) and, for tight dimensions, an uncertainty adequate for the tolerance.
- Who measured and when.
- Result: conforming or nonconforming, per dimension.
All dimensions or only critical ones? For a spare part, functional dimensions are enough: fit diameters, positions of holes that get assembled, flatness of seating faces. For tooling or a gage, a full report is worth it, because the tooling becomes the reference for other parts. If critical dimensions are not flagged on the drawing, flag them before quoting; otherwise the supplier picks what to measure.
When to require CMM measurement and when manual instruments are enough is explained in CMM metrology and quality control in high-precision machining.
5. The material certificate: heat number and document type
A useful material certificate identifies:
- The standard and grade (for example, AISI 4140, AISI D2, 6061-T6 aluminum).
- The heat or lot number of the material.
- The chemical composition and, depending on the material, mechanical properties (strength, as-supplied hardness).
- Who issues it: the mill or the distributor.
For metals, the document type is defined by the EN 10204 standard. The two most used:
| Type | What it is | What it is good for |
|---|---|---|
| 2.2 | Test report with results from non-specific inspection: typical data from the manufacturer's production | Non-critical spare parts |
| 3.1 | Inspection certificate with test results on the heat or lot delivered, validated by inspection independent of manufacturing | Tooling, critical spares, any part where the material is part of the function |
The point almost nobody checks: traceability down to your part. A 3.1 certificate for a heat is useless if nobody can show your part came from that bar. Ask for the certificate with the heat identified and for the supplier to be able to tie it to your order. A generic distributor certificate without a heat number is a datasheet, not a certificate.
6. Heat treatment and coating
If the drawing calls for a treatment, ask for evidence that it was done and of the result:
- Heat treatment certificate: treatment type, specification, furnace lot and measured hardness. What matters is the hardness measured on the parts (or on a test coupon from the same lot), not the target hardness copied from the drawing.
- Where hardness is measured. On hardened parts, surface and core hardness can differ. If the drawing calls for hardness in a specific zone (for example, the surface of a locating pin), the report must say where it was measured.
- Coating certificate: coating type, measured thickness and standard. Thickness matters when there are fits: hard anodizing or hard chrome adds material, and the drawing has to say whether dimensions apply before or after coating.
For tooling with hardened and ground parts (pins, bushings, wear plates), the heat treatment certificate matters as much as the dimensional report: a part with the right dimension and the wrong hardness wears out in weeks.
7. What happens if you do not ask before quoting
It is the most expensive mistake in this guide, and the most common. Three things happen:
- Some documents can no longer be produced. A material certificate with the heat number depends on the shop having recorded which bar it used; if it did not, nobody can reconstruct it. The heat treatment certificate depends on the furnace lot. And some internal dimensions cannot be measured once the part is finished or assembled.
- The cost was not in the price. Measuring and documenting takes lab time. Requested afterwards, it shows up as an extra charge or as an argument.
- The date moves. A full CMM report or a 3.1 certificate that has to be obtained from the distributor adds time nobody planned for.
The practical rule: write in the RFQ which documents you need and at what level of detail (critical dimensions or full, material certificate type, hardness and zone). If you are not sure, ask the supplier what they deliver by default before placing the order, not at receiving.
And as part of qualifying any supplier, it is worth asking for a sample of the documents they deliver. How to read a system certificate, and why it does not replace part evidence, is covered in how to verify a machining supplier's certifications.
If the part is aerospace, first article inspection follows the AS9102 standard, which defines what is documented and in what format. There the rule is even stricter: the FAI is done during production of the first part, not afterwards.
Frequently Asked Questions
Does a machined spare part need a PPAP?
Almost never. PPAP is the process for approving a series production part before it enters the customer's line. A maintenance spare part or a 1–10 piece tooling order is released with proportional evidence: a dimensional report, a material certificate and, where applicable, a heat treatment or coating certificate. The exception is when the spare part is a service part for a series automotive product: there the customer may ask for a service PPAP.
What should a dimensional report include?
The drawing number and revision, each measured dimension identified against the drawing (ideally a ballooned drawing with numbers), the nominal value and tolerance, the measured value, whether it conforms, the instrument used, and who measured it and when. A report that only says 'part conforms' with no measured values is not a dimensional report, it is a declaration.
What is the difference between a 2.2 and a 3.1 material certificate?
They are document types defined in the EN 10204 standard. A 2.2 is a test report based on non-specific inspection: the manufacturer declares the material complies and gives typical results from its production. A 3.1 is an inspection certificate with test results from the lot or heat being delivered, validated by an inspection representative independent of manufacturing. For tooling and critical spare parts, the 3.1 is the one that provides real traceability.
When should a spare part come with an FAI?
When the end customer or the industry requires it, typically aerospace, where the AS9102 standard defines how first article inspection is documented. It also makes sense for complex tooling that will be reproduced several times: the FAI of the first piece becomes the reference for the next ones. For a simple one-off spare part, a full dimensional report is usually enough.
What happens if I ask for the documents after receiving the part?
Some can no longer be produced. A material certificate with the heat number depends on the shop having kept traceability of the bar it used; a heat treatment certificate depends on the furnace lot; and some internal dimensions cannot be measured once the part is finished or assembled. On top of that, the cost of measuring and documenting was not in the quote. That is why documents are requested in the RFQ, not at receiving.
Conclusion: evidence that is not requested is not produced
Quality documentation for a spare part is not paperwork: it is what lets you answer, on the day something fails, what material the part was, what hardness it had and whether anyone measured the dimension that mattered. That does not take the series production package. It takes asking, at quoting, for the dimensional report of the dimensions that matter, the material certificate with the heat number, and the heat treatment certificate when it applies.
Radii makes spare parts and tooling through its network of shops audited for ISO 9001 and AS9100 compliance, and machines under IATF 16949 systems when the part is automotive. Parts ship with dimensional inspection and digital traceability certificates. Upload your drawing to Radii, state which documents you need, and the quote includes them.