How to Brief a Factory on Your Product Design (Without Confusion)

A factory quotes what you describe, not what you imagine. To get an accurate quote and a product built the way you designed it, send one complete package: CAD files (a STEP file plus a dimensioned PDF drawing), a full bill of materials, exact material and finish specifications, Pantone color references, tolerances on the features that matter, assembly and packaging instructions, your quantities, and your timeline. That is the whole design brief. The rest of this guide shows you how to assemble each piece so a factory in China can cost, sample, and build your product without guessing.

Most quoting problems trace back to missing information. A factory that receives a sketch and the words "high quality, black plastic" fills in the blanks with the cheapest options, and the sample arrives in the wrong material, the wrong shade of black, and three weeks late. At CN Ally, a China sourcing agent, the first job on any custom product is turning rough designs into a factory-ready brief before a single quote is requested. The brief below follows that same structure, and you can use it yourself.

Why the brief decides the quote you get

A vague brief does not get you a cheaper price. It gets you a fictional one.

When a factory cannot see your materials, tolerances, or finishes, it has two choices: pad the quote with contingency for every unknown, or price the cheapest possible interpretation to win your business and revise upward later. Buyers who send the same design to five factories with a thin brief routinely get quotes that differ by multiples, not percentages, because each factory priced a different imaginary product. A complete brief forces every factory to price the same real product, which is the only way quotes become comparable.

There is a second effect that matters more than price. Factories triage inquiries. A buyer who sends organized files, a BOM, and clear specifications signals a serious project that will move fast, and that inquiry gets answered by someone senior. A buyer who sends three phone photos and "please quote" gets answered slowly, if at all.

What a factory actually needs from you

Here is the full brief in one list. Each item below gets its own section with exactly what to include.

1. CAD files and drawings the factory can open
2. A bill of materials (BOM) covering every part
3. Material and finish specifications, named precisely
4. Colors by numbered reference, not by description
5. Tolerances on the features where they matter
6. Assembly instructions
7. Packaging and labeling specifications
8. Commercial terms: quantities, timeline, and target price

You do not need all eight perfected before first contact. You need enough for the factory to evaluate fit and quote accurately, with anything still open marked "to be confirmed." A brief that flags three undecided items beats one that pretends they are settled.

CAD files: send STEP, not screenshots

For 3D parts, send a STEP file plus a dimensioned PDF drawing. For flat parts like sheet metal, send a DXF plus a PDF. STEP carries the exact geometry the shop's CAM software needs, while the PDF carries everything geometry cannot express: tolerances, threads, finishes, notes (techdrawai.com). The accepted formats are standard across the industry (bayengineering.co.uk):

Format · What it is · When to send it

• STEP (.step, .stp): Neutral 3D format, exact geometry · Every 3D part
• IGES (.igs, .iges): Older neutral 3D format · Fine if that is what you have
• Parasolid (.x_t, .x_b), ACIS (.sat): CAD kernel formats · Accepted, less common from buyers
• Native files (SolidWorks, Inventor, CATIA, NX, Creo): Proprietary formats · Only if the factory runs the same software
• STL (.stl): Mesh of triangles, an approximation · 3D printing only, not CNC or molding
• PDF (dimensioned drawing): Human-readable drawing · Always, alongside the 3D file
• DXF (.dxf): 2D flat profiles · Laser cutting, sheet metal, patterns
• DWG (.dwg): AutoCAD's native format · Acceptable; DXF opens more reliably

Three rules make this work in practice. First, export STEP from whatever CAD software you use; it is the safest exchange format between different systems. Second, never send screenshots as a substitute for files. A screenshot shows the shape but gives the factory's machines nothing to work with. Third, put dimensions and tolerances on the PDF drawing, not only in the 3D model. Geometry shows the shape. The drawing shows what the shape must achieve.

Draw in millimeters and state the units; China works in metric. Keep drawing text short, in plain English, with numbered callouts pointing at features. Short, numbered, and visual beats long and verbal.

The bill of materials: the factory's shopping list

A BOM is the complete list of everything in one unit of your product: every part, material, fastener, label, and the packaging. If it ships in the box, it belongs in the BOM. Without one, the factory sources what seems reasonable, and reasonable varies by factory. Build it as a table with these columns:

Column · What goes in it · Why the factory needs it

• Part number: Your internal code, e.g. WD-001 · One identifier both sides can point to
• Description: Plain name of the part · Distinguishes similar parts
• Quantity per unit: How many per finished product · Drives purchasing and cost
• Material and specification: Exact grade, standard, or datasheet · The difference between guessing and knowing
• Source: Buyer-supplied or factory-sourced · Decides who owns the lead time
• Critical notes: Finish, tolerance class, approved alternates · Where your non-negotiables live

The "source" column deserves attention. Some buyers supply key components themselves, like branded chips or certified fabrics, while the factory sources the rest. Mark each line clearly. Where the factory sources, state whether it may substitute an equivalent material or must buy your approved brand. Unapproved substitution is one of the most common sources of sample-to-production drift: the approved sample uses your specified material, and mass production quietly switches to a cheaper equivalent. Write the approval rule into the brief and the ambiguity disappears.

Include packaging in the BOM, not as an afterthought. Retail boxes, polybags, inserts, barcodes, and shipping cartons all have specifications, lead times, and costs. A product brief that forgets packaging discovers the omission when the finished goods have nowhere to go.

Materials, finishes, and colors: name everything precisely

"Black plastic" is not a specification. It could mean ABS, polycarbonate, nylon, or a dozen other resins, each with different strength, cost, and surface behavior. Name the exact material: the resin grade, the metal alloy and temper, the fabric composition and weight. If you reference a standard or a supplier datasheet, attach it.

Finishes need the same precision. Matte black can be molded texture, paint, or powder coat, each a different process and price. State the process and the result: "powder coat, matte, 60 to 80 gloss units." Where the finish affects function, say so. Anodizing on aluminum is partly cosmetic and partly corrosion protection.

Colors should be specified by number, not by adjective. Pantone is the color reference system most factories and brands share: you name a Pantone code, the factory mixes or matches to it, and both sides judge the result against the same standard. For textiles and leathers, where dye lots vary, a physical color swatch approved by both sides works better than any code. Either way, the color must exist as a shared physical reference, not as a word in an email. "Navy," "cream," and "rose gold" mean different things to different people, and a factory cannot match a meaning.

One practical note: colors shift under different light. If accuracy matters, state the evaluation lighting, such as daylight, in the brief.

Tolerances: specify the critical few

Tolerances tell the factory how much a dimension is allowed to vary. The beginner mistake is specifying tight tolerances everywhere, which raises machining cost and inspection time without improving the product. Mark tight tolerances only on the features that need them, like mating surfaces, seals, and threads, and let general tolerances cover the rest.

Your PDF drawing should show the critical dimensions with their tolerance bands, for example "25.00 ±0.05 mm" on a shaft that fits a bearing, while cosmetic outer dimensions carry no special callout. Factories apply their own general tolerances to unmarked dimensions. Ask what their standard is, or state the tolerance class you require, so both sides share the same default. This is also where your specification document earns its keep: our guide to writing product specifications for QC shows how tolerances flow from the brief into inspection criteria.

Test every tolerance: can you explain what breaks if this dimension drifts? If nothing breaks, loosen it. Every unnecessary tight tolerance is money spent on precision nobody will notice.

Assembly, packaging, and reference samples

Assembly instructions do not need to be a manual. An exploded-view diagram with assembly order, fasteners, adhesives, or torque values is enough for quoting and the first run. A thirty-second video of you assembling the prototype says more than two pages of text. If the factory assembles, state who supplies the jigs and fixtures.

Packaging deserves a specification of its own: retail box dimensions and material, inserts, polybag thickness, barcode placement, and the shipping carton spec with its markings. Packaging has its own tooling, like cutting dies, and its own lead time. Treat it as a small product inside your product.

Reference samples are the part of the brief no drawing can replace. When color, texture, weight, or feel matters, mail the factory a physical sample and write its role into the brief: "match this color," "match this surface feel," "this is the minimum acceptable quality." The approved pre-production sample then becomes the reference that inspections are judged against, a process our prototyping guide walks through in detail. A drawing says what the product should be. A sample shows what it should feel like. Send both.

Ask these before the factory starts

A good brief is also a conversation. Before the factory begins sampling or tooling, get answers to these five questions in writing.

What is still unclear in this brief? The factory's questions are a free audit of your documentation. If three factories ask about the same missing dimension, the gap is in your brief.

Which tolerances can you hold in-house, and which need a subcontractor? A factory that outsources precision work is not disqualified, but you should know which steps leave the building. Every handoff is a quality risk.

Who sources each BOM line, and may you substitute materials? Get the substitution rule in writing now, while it is cheap to agree on. This sentence prevents sample-to-production drift.

What does your first-article and pre-production sample process look like? You want to hear a defined approval gate: sample made, measured against the drawing, sent to you, approved in writing before production. If sampling is informal, production will be too.

What happens to tooling, molds, and files if we part ways? Molds you paid for should be releasable to you, and your CAD files should not be reused for other customers. Agree before money changes hands, not after the relationship sours.

Your copy-paste factory design brief checklist

Use this as the cover sheet of the folder you send.

1. Product name, your company, and one-paragraph product description
2. Target quantities: first order and expected annual volume
3. Target timeline: sample date, production date, delivery date
4. Target price range, if you have one, marked as a target not a ceiling
5. 3D CAD files in STEP format for every custom part
6. Dimensioned PDF drawings with tolerances on critical features
7. DXF files for any flat parts: sheet metal, gaskets, fabric patterns
8. Complete BOM: every part, material, fastener, label, and packaging item
9. Material specifications: exact grades, alloys, fabric compositions
10. Finish specifications: process plus measurable result
11. Color references: Pantone codes or approved physical swatches
12. Assembly instructions: exploded view, order, fasteners, adhesives
13. Packaging specification: retail box, inserts, polybag, carton, markings
14. Reference samples mailed, with their role written down
15. Certifications or testing the product must pass, if any
16. Items still open, marked "to be confirmed," with dates for decisions

Sixteen items take an afternoon to compile and save weeks of clarification emails.

Frequently asked questions

What CAD file format should I send to a manufacturer?

Send a STEP file (.step or .stp) for 3D parts and a DXF for flat parts, each paired with a dimensioned PDF drawing. STEP is the most widely accepted neutral 3D exchange format: the factory's CAM software reads exact geometry from it. The PDF carries what geometry cannot, including tolerances, threads, surface finishes, and notes. Avoid sending only STL files for machined or molded parts. STL describes the shape as a mesh of triangles, which works for 3D printing but is an approximation that precision manufacturing cannot work from directly.

What should be in a factory design brief?

The eight essentials: CAD files and drawings, a complete bill of materials, exact material and finish specifications, numbered color references, tolerances on critical features, assembly instructions, packaging specifications, and commercial terms covering quantities, timeline, and target price. Add reference samples when color or feel matters, and mark anything still undecided as "to be confirmed."

Do I need a BOM if the factory sources everything?

Yes, even more so. When the factory sources, the BOM defines what "everything" means. Without it, the factory chooses materials by its own judgment, and you discover the choices at the sample stage or, worse, in mass production. A BOM with a written substitution rule, approved suppliers or equivalent grades, and clear buyer-versus-factory sourcing responsibility keeps the production you receive matched to the sample you approved.

How do I specify colors for manufacturing in China?

By number, not by name. Use Pantone codes for plastics, coatings, and printed packaging, and confirm the factory can match to Pantone references. For dyed textiles and leathers, approve a physical swatch and keep a sealed copy yourself as the reference standard. State the lighting condition for color evaluation when accuracy matters. Never rely on a screen photo: the same color renders differently on every display.

I don't have CAD files yet. Can I still get a quote?

You can get a rough estimate from sketches, reference products, and dimensions, but not a firm quote. Factories price geometry, materials, and processes, and a sketch leaves all three open to interpretation. If your design is still an idea or a sketch, do product development first: CAD modeling, then a prototype, then the brief. That sequence is exactly what our product development service handles for buyers who need engineering support before approaching factories.

Should I share design files before signing an NNN agreement?

Get the agreement signed first. CAD files are your intellectual property in its most usable form: a factory holding your STEP files can manufacture your product without you. A China-specific NNN agreement, covering non-disclosure, non-use, and non-circumvention, should be in place before files change hands. Our guide to NNN agreements in China explains what it should contain and why a Western-style NDA is not enough.

The read-back test

Here is the decision rule that replaces a conclusion. Before you approve a quote, a sample, or a production run, ask the factory to restate your brief back to you: materials, tolerances, colors, quantities, timeline. Where their restatement matches, you have understanding. Where it differs, you have found the next revision, and finding it now costs nothing.

A design brief is not paperwork for its own sake. It is the cheapest quality control you will ever buy, because every confusion it prevents would otherwise surface as a wrong sample, a delayed shipment, or a container of products you cannot sell. Write it once, write it completely, and make the factory prove it understood.

If your product is still a sketch and a folder of reference photos, that is a fine place to start, and it is exactly where a sourcing partner earns its keep. CN Ally turns rough designs into factory-ready briefs: documentation, BOM structuring, and supplier matching in China, so the quotes you receive describe one real product. Write to hi@cnally.com with what you have, and we will tell you honestly what is missing before any factory sees it.