If you have customers who have difficulty threading fine needles this could be a solution, such as Au Ver a Soie, Soie 1003 and Crewel/Embroidery needle size #10. It sits on a table, and you place your needle eye facing downwards in one of the two slots provided. The slot without the ridge is the best choice for the finest needle. Lay the fine thread in the crevasse next to the slot and push firmly on the center black button. The needle is then threaded. This will not work for needles with round eyes, but works for oval-eyed needles such as Betweens, Sharps, Milliners and Crewel/Embroidery. A great demonstration for a embroidery class teaching metal thread couching, for example.
