The operation of double-lock metal handcuffs is as follows: - 1. A mechanism that locks the handcuff pawl in the engagement position and prevents the ratchet from further advancing in the closing direction. 2. The ring shackle on the wrist is usually one of a pair connected by a short chain or connecting rod. 3. A spring-loaded pivot bar that engages with the teeth of the ratchet and only allows the ratchet to move forward in the closing direction. 4. A rod with inclined teeth is designed to engage with the pawl. The ratchet shall move freely through the pawl in only one direction of movement. 5. Weight: no more than 425 g (15.0 oz) 6. Material: rust-proof stainless steel. 7. Size: The minimum opening of each pair of handcuffs is 50 mm (2.0 inches) for insertion into the wrist. When the ratchet is engaged at the first notch of the locking mechanism, the inner circumference of the handcuffs shall be at least 200 mm (7.9 inches). When the ratchet is engaged in the last notch of the locking mechanism, the maximum inner circumference of the handcuffs is 165 mm (6.5 in). The maximum total length of handcuffs is 2400 mm (9.4 inches). 8. Mechanical strength: during the test, the maximum tensile force of 2200 N (495 lbf) can be borne for each corresponding part, and the duration shall not be less than 30 seconds. It does not open under load, has no sign of permanent deformation or fracture, and operates in a normal manner after the test. 9. Corrosion resistance: when exposed to salt water spray, there will be no substantial corrosion and continue to work normally.

Plate handcuffs and chain handcuffs are two common forms of handcuffs, and the main difference lies in the connection of handcuffs. Chain handcuffs are an early design, with 2 to 3 iron rings connected in series between the handcuffs. Although this design shackles people's hands, the radius of movement formed by the length of the chain is still quite long, and the handcuffed person is still very convenient in action.