For the 2014 season and beyond, NHRA has made the following requirement:

All removable multipiece exhaust collectors/stacks must be securely fastened with either an NHRA-accepted header tether or a minimum ½” (half-inch) stitch weld located on each primary tube to prevent loss of collector/stacks during competition.

After much discussion on the topic, it has been decided that on cars with a complete exhaust system (including but not limited to mufflers, hangers, flanges, etc.) that are securely attached to the vehicle, header tethers will not be required.  All other exhaust systems must conform to the rule as written.  The current 2014 rulebook will be amended to reflect this change.