Dimensional Tolerance Testing for Precision Machined Parts from China

The most common quality problems I've seen across thousands of inspections are: (1) dimensional deviation — products not matching spec measurements, (2) color variation — especially between sample and bulk, (3) surface defects — scratches, dents, rust, (4) packaging damage — inadequate protection, wrong materials, (5) mix of good and defective units in the same carton. A solid QC plan addresses all five.

Material substitution is a common issue in China manufacturing. The factory may use a different grade of steel, a different type of plastic, or a different fabric than specified — usually without telling you. This often happens when the specified material is out of stock or more expensive. Protect yourself by: specifying brands or grades, requesting material certificates, conducting random material testing, and including a clause in your contract that unauthorized material changes void the quality guarantee.