CFR › Title 7 › Part 51 › §51.21237 CFR §51.2123Verified against eCFR.gov as of June 20, 2026View official text on eCFR.gov ↗Copy linkForeign material means pieces of shell, hulls or other foreign matter which will not pass through a round opening 8/64 of an inch (3.2 mm) in diameter.