Gst rate for job work

https://www.taxmanagementindia.com/visitor/detail_article.asp?ArticleID=7419&kw=JOB-WORK-AND-JOB-WORKER-UNDER-GST-REGIME-PART-1

From what I understand, if the turnover is less than 20Lakhs no tax and if it is below 75Lakhs one may opt for Composition and if iot above it is 18%.

Dear Sir

What is the SAC Code for Powder Coating Works