Start Preamble AGENCY: Bureau of Alcohol, Tobacco and Firearms (ATF), Department of the Treasury. ACTION: Final rule, Treasury decision. SUMMARY: The Bureau of Alcohol, Tobacco and Firearms (ATF) is amending the regulations to prescribe minimum height and depth requirements for identification markings placed on firearms by licensed importers and licensed manufacturers. Specifically, we are requiring a minimum height of 11/16 inch and a minimum depth of.003 inch for serial numbers and a minimum depth of.003 inch for all other required markings.