Analysis
NAICS 3151 is the 2022 industry group for apparel knitting mills, part of 315 (Apparel Manufacturing).
It has only one more detailed code, 315120, which covers exactly the same activities; the definition, index entries and statistics are on that page.
County Business Patterns counts 178 US establishments in this code in 2023, employing 7,656 people at an average annual payroll of $37,870 per employee (7th percentile of national industries). 31% of the establishments have fewer than five employees, which is close to the national mix.
Between 2018 and 2023 the number of establishments fell 18% and employment fell 29%. The 2018 count used NAICS 2017, so part of a large move can come from codes being redefined rather than from businesses opening or closing.
By establishments it ranks 3rd of the 3 codes at this level within Apparel Manufacturing, with 4.1% of them.
Its goods appear in 52 statistical lines of the US tariff schedule, mostly under headings 6115 (panty hose, tights, stockings, socks and other hosiery…), 6117 (other made up clothing accessories, knitted or crocheted…) and 6505 (). That link is how import data is matched to domestic producers, for example in trade-remedy cases.