These handcuffs double lock by using a padlock through a hole in the jaw and the pawl. This requires the officer to carry padlocks (two) in order to double lock but it does add a level of security other handcuffs don't possess. The cuffs are made from aluminum but are quite strong. The key is a barrel key with relatively thin walls which makes picking somewhat diffecult. They are also tricky to shim. Made in Baden-Wuerttemberg (one of Germany's Countries) they were in use during the 1940's - 50's.