[Code of Federal Regulations] [Title 49, Volume 2] [Revised as of October 1, 2005] From the U.S. Government Printing Office via GPO Access [CITE: 49CFR179.100-17] [Page 1041] TITLE 49--TRANSPORTATION CHAPTER I--PIPELINE AND HAZARDOUS MATERIALS SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION PART 179_SPECIFICATIONS FOR TANK CARS--Table of Contents Subpart C_Specifications for Pressure Tank Car Tanks (Classes DOT-105, 109, 112, 114 and 120) Sec. 179.100-17 Closures for openings. (a) Closures shall be of approved design and made of metal not subject to rapid deterioration by the lading. Plugs, if used, shall be solid, with NPT threads, and shall be of a length which will screw at least six threads inside the face of fitting or tank. (b) [Reserved]