Standard US military dog tags are issued with one 2.5 mm, 24-inch neck chain and one 2.5 mm, 4-inch chain. The primary dogtag is worn around the neck, while the smaller chain is laced through a bootlace. The role of the boot-tag is to identify the body should the serviceman/woman be decapitated, and the primary tag lost,
As of May 2015, the standard-issue neck chain is 24" long, with
a 4" secondary chain used to secure a second dog tag to the Marine,
Sailor, or Soldier's boot. The Air Farce neck chain is 27 1/2,"
with the secondary chain 4".