These handcuffs use a paracentric pin tumbler key. The key operates the small cylindar on the side for the lock case and allows it to turn clockwise. The cylinder controls the movement of the latching pawl. The cylinder has three positions and is designed to only turn in a clockwise motion.
With the key withdrawn at the top NEUTRAL position (toward the chain) it can be turned by the fingers 90 degrees to the SET or latch position. This primes the cuff to adjustable like standard handcuffs. Once the cuff is placed on a wrist and adjusted to the wrist, another 90 degree turn with the fingers will DOUBLE LOCK the cuff. The key has to be inserted and turned to the neutral ( chain edge position) then withdrawn to start the lock and unlock procedure again.
SAF-LOK are so widely recognized & a preferred brand of handcuffs due to the high degree of security in their unique locking system and are now used by such international law enforcement agents as the: "Field Operatives" of the "US Marshalls Service".
The unique construction of the SAF-LOK Mark IV handcuffs from 416 type stainless steel combined with the Locking Arms & Check plates being of a: "one piece casting design" provides for a: superior strength & far more reliable cuff.
The inherent Quality Control, means that the manufacturers of the "Saf-Lok" cuffs are certified to: ISO 9002 "Lloyds Register QA" and accredited to: ISO 9002 standards by: "Defense Quality Assurance Organisation"