Keeps your bobbins organized on top of colour matching thread spools. Compatible with most bobbins and most brands of home embroidery and sewing thread spools,(not intended for large commercial or jumbo spools)Made of quality silicone that adjusts to different thread spool diameters, fits on spools openings from 0.25" (6mm) to 0.5" (13mm)Wind thread twice over post before snapping on bobbin, to prevent unwinding.Colourful and functional! They will make your sewing life easier.