Rather similar to the Berliner Handcuffs, these are somewhat slenderer and sleeker. There are no obvious seams in the lock mechanism.
Quoted from a recent sale on eBay:
This is a Mühlenfeld No.113 handcuff, among collectors also known as "The Dortmunder"!
At the end of the 19th until the beginning of the 20th century the August Mühlenfeld Company produced restraints, but also holsters, belts, sabres and other police equipment. The firm was placed in a small town with the name "Barmen", Mühlenfeld cuffs are stamped not only with the company name but also with the name of this town. In 1921 this town co-operated with four other small towns and they founded the city of Wuppertal. Today there are no traces of this company left.
Regarding the design of the restraint,one could say that it belongs to the Berliner family of handcuffs: the two moveable bows of the cuff engage into one common lockcase which is in the center of the cuff, there is a singular key-hole through which the two bows are released.