Put Quality in Writing, Not in Words
Spec Sheets, Drawings & BOM for China Manufacturing

Hello, this is GreenFrog Seoul.

"I worked it all out with the contact over WeChat, but when mass production came in, the color was off and the thickness had gotten thinner."
"The sample was perfect, so why is the bulk run like this? I wanted to push back, but I had no basis to stand on."
"The factory says 'the customer never told us that,' and I say I clearly did — and in the end I ate the loss."

Trace where quality accidents happen in China sourcing and, far more often than the factory being incompetent, the cause is that what to make was never locked down in writing. Agreements traded verbally, over WeChat, or with phrases like "same as last time's sample" vanish without a trace once the person changes and time passes. The factory fills that empty space in whatever way suits it — cheaper material, thinner walls, sloppier finishing.

Here's the point up front: quality is not something you negotiate — it's something you instruct in writing. Three documents — the spec sheet, the drawing, and the BOM (bill of materials) — nail down "the product I want" with no room for misreading. With them, you can push back with evidence when mass production goes off; without them, no matter how wronged you feel, all that remains is a claim that "I said so." Today we walk through what to put in these three documents, in the order you'd actually use them.

We covered molds (#33), sampling (#34), and the quality control system (#21) separately before. Today's piece focuses on the "documentation" that sits underneath all of them. Only when what-to-make is fixed on paper do samples, inspection, and molds finally have a standard to hold to.

1. Why Verbal & WeChat Promises Don't Lock In Quality

Chatting with a factory over WeChat, in the moment everything feels agreed — after all, you get "Yes, understood" and "No problem" back. But as we noted in #41, that conversation fails to hold quality in place for a few reasons.

• Words leave wide room for interpretation — "Sturdy," "premium," "a bit thicker than last time" read differently for each person. An adjective not nailed down with numbers and specs gets read in whichever direction is cheapest to make
• The contact person changes — The sales rep who quoted, the production manager who actually runs the line, and the QC who inspects are all different people. Nothing guarantees a promise made with sales over WeChat reaches the production line
• Records scatter — WeChat threads mix into hundreds of messages and scroll away out of reach. When a dispute finally erupts, you end up hunting for "that message where we discussed the color"
• It can't serve as evidence — To file a claim (#36), you have to show the gap between "the agreed spec" and "the actual goods." Verbal promises can't build that comparison

2. The Spec Sheet — What It Must Contain

A spec sheet is the document that defines "what this product is" on a single page (or a few). There's no fixed template, but if the items below are missing, that's exactly where the seed of a quality accident is planted. Let's take them one at a time.

Dimensions and tolerance — the "number" and the "allowed range" together

Dimensions don't end with writing a number. You must write the tolerance (allowable error) alongside. Write only "width 100mm" and there's room to argue that both 99mm and 101mm are "fine." Set a range like "100±0.5mm" and anything outside it is a clear defect. The more a product is assembled from parts or must fit precisely, the more this one line of tolerance decides whether the mass run succeeds or fails.

Material and color — by code, not by name

Material should be written down to the grade, not a broad bucket like "plastic" or "stainless." The same ABS differs in strength and smell between virgin and recycled; the same stainless differs in rust resistance between SUS201 and SUS304. For color, as we detailed in #45, specifying by Pantone number is the safe route. "This blue" seen on your monitor looks different on the factory's monitor, and different again once it lands on the actual material. You need a shared language — a Pantone chip — to cut down fights over color.

Inspection criteria and AQL — the link from spec sheet to inspection

The last cell of the spec sheet should be the inspection criteria. Define where the line of "defect" sits (scratches over X mm, color variance over Y degrees) and connect it to an AQL level. Only with this item does the third-party inspection covered in #47 know "on what basis to split pass and fail." The spec sheet effectively becomes the original of the inspection checklist.

3. Drawings — Your Response Depends on What You Have

A drawing is the document that fixes the spec sheet's numbers as a "picture." It shows the shape, the dimensions at each spot, cross-sections, and how parts assemble, all to the eye. The catch is that most beginner sellers don't have a proper drawing. So it's more realistic to approach drawings not as "have one or not," but as how to respond to the level you have.

2D drawings and 3D data, each with its role

2D drawings are strong at stating dimensions and tolerances clearly. Split into front, side, and section views with an allowable error on each dimension, you can check against them directly during inspection. 3D data (STEP, IGES, etc.) is strong at conveying shape without misreading, and a factory cutting a mold (#33) can put it straight to work. The two aren't rivals but complements — if you can manage it, handing over shape in 3D and dimensions/tolerance in 2D together leaves the least room for misunderstanding.

When you have no drawing, only a reference sample

This is the far more common situation in practice. You couldn't draw anything, but you have a similar product bought off the shelf or a sample received before. Here, the method that works well is to make the physical sample itself the standard for the spec, while spelling out only the parts you want to change in writing.

• Designate a reference sample — Make "identical to this sample" the starting point of the spec. Send the factory the physical item and keep a record — photos, a shipping receipt — that you did
• Pin down only what changes — List the changes like "identical to the sample, but color to Pantone 285C, thickness from 2mm to 3mm, remove the logo." Everything else means: follow the sample
• Write dimensions onto photos — Even without CAD, drawing key dimensions and arrows onto a photo of the sample makes a fine quick drawing. Even a hand sketch becomes evidence once numbers are attached

4. The BOM — Preventing Missing Sub-Materials, Printed Matter, and Accessories

The BOM (bill of materials) is the document that lists every material and part making up the product. It's easy to picture only the main body, but the spot where accidents actually happen is usually a sub-material you forgot — the manual, a sticker, the warranty card, screws, a pouch, a silicone stopper. If these are missing from the BOM, they're missing from the quote, and missing from mass production.

Write the BOM properly and you get a bonus: the cost structure becomes visible. Once each material's quantity and unit price are lined up row by row, it shows which part is pushing up cost and where you could adjust to lower it. At the negotiating table (#38), you can ask, item by item, "how much comes off if we drop this accessory to an option?" That's far stronger than wrestling over one lumped-together price.

5. Version Control and the Link to the Production Approval Sample

Even if you build the documents well, if you don't manage which version they are, confusion sets in fast. Sourcing doesn't finish in one shot, and the spec keeps shifting a little through the discussion. If you can't confirm that "the version where we agreed to raise thickness to 2.5mm" matches the file the factory holds, you get the accident where you mean v3 but the factory builds v1.

• Stamp a version number and date on the document — Put "v2.1 / 2026-07-09" in the spec sheet, BOM, and drawing filenames and inside the documents, so it's obvious at a glance which is the latest
• Keep a change log — Leave a one-line note on what changed and why. It becomes the basis when you later retrace "why did this thickness end up like this"
• Confirm the version the factory holds — When you send a new version, nail down "scrap the previous version and work to v2.1," and get back the factory's confirmation that it checked against that version

The end point of this document management is the production approval sample. The "golden sample" covered in #34 meets you here. Once both sides check and approve a sample made to the final spec (the latest-version spec sheet, BOM, and drawing), that sample becomes the physical standard mass production must hold to. If documents fix the spec in numbers, the approval sample fixes what that document looks like made real. Keep the two together and, when mass production goes off, you can lay both the documents and the sample on the table as evidence.

6. Chinese Alongside — A Small Habit That Cuts Misreading

However well-built the document, if the factory's contact can't read it, only half gets through. A Chinese factory's production line, handed a spec sheet only in English, easily mistranslates or skips key terms. So the habit of putting Chinese alongside at least the key items makes a big difference.

• Put decisive terms — material, finishing, color — in Chinese too — e.g., virgin ABS (全新料ABS), matte painting (哑光喷涂), Pantone 285C (潘通285C). Start with the items where a mistranslation turns straight into an accident
• Leave numbers and units as they are — Figures and units like 100±0.5mm are universal and need no translation. It's safer, in fact, not to touch them
• Lay Korean/Chinese side by side in a table — Korean (or English) on the left, Chinese on the right, so both sides can cross-check. If translation quality worries you, breaking things into short, clear sentences as covered in #41 cuts mistranslation

7. Common Failure Cases — Where the Document Was Left Blank

Case 1 — No tolerance written, so assembly failed

A seller ordered a product where two parts fit together, wrote only each part's dimensions, and left out the tolerance. The factory made each part "to dimension," but one came out at +0.8mm and the other at −0.6mm, and they wouldn't fit. Individually both were "normal," so the factory wouldn't admit fault, and the seller — having failed to specify the tolerance — had no basis. In the end they split the rework cost down the middle.

Case 2 — "Just like last time" that triggered a material swap

This was a reorder (#37) where the seller conveyed only "make it just like the last order." In the meantime raw material prices had risen, and the factory quietly switched to a low-grade material that looked similar on the surface. Had the material grade been stamped as a code on the spec sheet, the swap would have been caught immediately — but "just like it" gave nothing to compare against. The problem only came to light after customer claims arrived.

Case 3 — The Korean labeling sticker left out of the BOM

The product body and packaging were perfect, but the Korean labeling sticker wasn't in the BOM. Having never been instructed, the factory naturally didn't apply it, and the goods cleared customs yet failed to meet the requirements for domestic sale (#46) and sat stuck in the warehouse. Applying stickers domestically after the fact cost extra money and time. That was the price of one blank line in the BOM's printed-matter cell.

The three cases share one thing, clearly: it wasn't that the factory was bad, but that the factory filled the blank the document had left in its own way. One line of tolerance in the spec sheet, one line of material code, one line for printed matter in the BOM — with any of them, none of the three would have happened.

8. Pre-Order Documentation Checklist

Spec sheet

• Wrote a tolerance (±) alongside every key dimension
• Specified material down to grade/code (virgin/recycled distinction included)
• Set color by Pantone number or color chip, and noted matte/gloss
• Made surface finishing and print method and position clear
• Connected inspection criteria (defect definitions) to an AQL level

Drawing / sample

• Prepared whichever I can of 2D (dimensions/tolerance) and 3D (shape)
• If no drawing, designated a reference sample and spelled out only the "changes" in writing
• Wrote key dimensions onto sample photos to make a quick drawing

BOM / version

• Listed everything down to sub-materials, printed matter, and packaging — not one line missing
• Included the Korean labeling sticker in the BOM
• Stamped a version number and date on every document, and confirmed the version the factory holds
• Kept the production approval sample made to the latest spec together with the documents

Closing — Quality Holds Only as Far as It's Written Down

Today's content, compressed one line each:

• Verbal / WeChat promises: they vanish when the person changes, and the factory fills the blanks on the low-cost side
• Spec sheet: nail down dimensions & tolerance, material code, Pantone color, finishing, function, packaging, inspection criteria & AQL
• Drawing: dimensions in 2D, shape in 3D. No drawing? Respond with a reference sample plus spelled-out changes
• BOM: it's done only when it reaches down to sub-materials, printed matter, and packaging — and it reveals the cost structure as a bonus
• Version / sample: document → approval sample → mass production must connect on the same version to be managed on one standard

In China manufacturing, quality isn't protected just by meeting a good factory. What gets protected is exactly as much as you wrote down. The tighter the three documents — spec sheet, drawing, BOM — the less room mass production has to go off, and even if it does, you can set it right with evidence in hand. If you're unsure where to start putting your product's spec in writing, or how to build an instruction sheet when all you have is a reference sample, feel free to reach out.