[Code of Federal Regulations] [Title 49, Volume 2] [Revised as of October 1, 2006] From the U.S. Government Printing Office via GPO Access [CITE: 49CFR179.400-7] [Page 1100] TITLE 49--TRANSPORTATION CHAPTER I--PIPELINE AND HAZARDOUS MATERIALS SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION PART 179_SPECIFICATIONS FOR TANK CARS--Table of Contents Subpart F_Specification for Cryogenic Liquid Tank Car Tanks and Seamless Steel Tanks (Classes DOT-113 and 107A) Sec. 179.400-7 Tank heads. (a) Tank heads of the inner tank and outer jacket must be flanged and dished, or ellipsoidal. (b) Flanged and dished heads must have-- (1) A main inside dish radius not greater than the outside diameter of the straight flange; (2) An inside knuckle radius of not less than 6 percent of the outside diameter of the straight flange; and (3) An inside knuckle radius of at least three times the head thickness.