After years of processing RFQs from European and North American buyers, these are the five drawing specification gaps that most commonly cause rejected shipments or ambiguous orders from Chinese metal fabrication suppliers.
1. Missing or Ambiguous Surface Finish Specification
“Powder coat” is not a specification – it is a category. Without specifying RAL color, gloss level (matt, satin, or gloss), coating thickness (typically 60-80 micrometers), and whether dimensions are pre or post-coat, you get the supplier’s default interpretation. Full specification example: “Powder coat RAL 9005 jet black, 70-90um, satin finish (30-50 GU), dimensions apply before coating.”
2. No Material Grade on Drawing
“Stainless steel” ordered from China will arrive as 304 unless specified otherwise. If your application requires 316 for corrosion resistance, or 316L for welded assemblies, this must be on the drawing. Similarly, “aluminum” defaults to 6061 – but if you need 5052 for formability or 7075 for strength, specify it. Material grades are engineering requirements, not assumptions.
3. Weld Symbol Standard Not Specified
ISO and AWS weld symbols are similar but not identical. Chinese factories primarily follow GB standards (which mirror ISO). If your drawing uses AWS symbols, note this explicitly: “Weld symbols per AWS A2.4.” Alternatively, provide a weld detail sketch showing throat size, length, and pitch in millimeters rather than relying solely on symbolic notation.
4. Threaded Hole Standard Not Identified
A US buyer writing “8-32 thread” may receive metric threads if the supplier assumes the intent. Specify clearly: metric or unified, and for metric, specify pitch explicitly (M8x1.25 vs M8x1.0). If UNC/UNF threads are required, note this prominently – some Chinese shops do not stock inch-thread taps and must source them specially.
5. Deburring and Edge Condition Unspecified
Laser cutting and punching produce burrs. Whether parts are deburred depends on whether it is specified. If parts will be handled without gloves, or if sharp edges create a safety or fit issue, specify: “All edges deburred, maximum residual burr 0.1mm” or “Edges broken 0.3×45 degrees.” Without specification, deburring may or may not be applied depending on the factory’s standard practice. At Conwhole Hardware, we flag these gaps during our DFM review. Send us your drawings for a free review.