TCH developed their twin locking system in 2013.  The range of handcuffs is a revolution in handcuff design in that each pair now has two completely separate locking mechanisms.  In order to have enough space inside, the Baltimore Road engineering team had to keep designing and redesigning with a number of teething problems (pun ended!) until they finally got it right.  The new design means that each swinging arm now has 23 rather than 25 ratchet bars.  All TCH models comply with the new draconian NIJ standards which came into force in October 2017