Normal inspection: sample size is 50, 0 to 1 back
The more stringent inspection: sample size is 50, 0 to 1 back
Relaxation of the test, the sample size is 20, 0 to 1 back.
The specific method can refer to the national standard "Technical Sampling and Inspection Procedures Part I: Sampling Plan for Lot-by-Lot Inspection by Accepted Quality Limit (AQL) Retrieval". There are detailed tables inside.