What is "tjasker"

The tjasker (Frisian: jasker, German: Fluttermühle) is a small type of windmill used solely for drainage purposes. It is distinctive for its simple construction, featuring only a single inclined shaft that carries the sails on one end and an Archimedes' screw on the other, in this way avoiding the need for any gearing. The tjasker is commonly known as a typical Frisian windmill though it is also found in other Dutch provinces and in north Germany.