What an excellent design.  The story goes that the Americans supplied some old WW1 surplus Harrington and Richardson handcuffs to the Chiang Kai Chek regime in their struggle with Mao Tse-Tung and when they ran out the Chinese copied them and the rest is history.  These used to be double locking handcuffs but an observant customer recently (2021) observed that this is no longer the case. As they are now sealed inside a plastic bag I cannot test them individually. 

They are ingeniously designed with a key hole which is only exposed when the chain is canted at right angles.  The key is like a female spanner with an unusual shape which engages a good inch inside.  Very difficult to pick and impossible to shim as the bow, when engaged, drives a small wheel, not a ratchet.  They weigh 474 grams and range from 80mm to 45 mm diameter, depending on which of the 24 locking positions you choose. They are no longer supplied with a cheap faux leather pouch!