The HANS has a tether with a metal clip that engages fasteners that are permanently attached to the helmets. Description may not be perfect. Keith Averill can fine tune it if he is looking here. He can also put the attachment parts on helmets if they are needed.
Dr. Sheldon Cooper "The best # is 73. Why? 73 is the 21st prime #. Its mirror (37) is the 12th and its mirror (21) is 7 times 3
In binary, 73 it's a palindrome, 1001001 backwards is 1001001." like racecar
From the 73rd episode of Big Bang Theory