Abstract: A spinneret holder has a pressurizable chamber formed between a cupped base part having a rim centered on an axis and a cover part having a periphery snugly interfittable with the rim. A plurality of spinnerets is provided in the cover part so that a mass to be spun can be introduced into the chamber and exit as filaments from the spinneret. A rod or bolt lying on the axis has threads anchored in one of the parts and the other part is formed at the axis with the throughgoing holes through which the rod passes. Thus an element such as a head or nut on the rods bears axially on the other part and can press the rim of the base part nad periphery of the cover part axially tightly together.