Prewound bobbins

100% polyester 

Art no. 307 Royal Pre-wound - Packs of 144 pieces with 120 m spools.
Versatile, paper-sided pre-wound bobbins, particularly beneficial for multi-head embroidery machines. Fast, ready to use and convenient. The constant thread quantity and tension in each bobbin helps with production planning, as replacements of multiple bobbin threads at the same time and without waste becomes possible.

Art no. 310 Magna Glide prewound bobbin on magnetic core. - Packs of 100 pieces with 120m spools.
WHY THIS UNDER THREAD? So that you no longer have to worry about tension yourself. Once you have set the correct tension on the bobbin case after inserting the lower bobbin, the bobbin will unwind smoothly and evenly to the end.

Oeko-Tex Certification

Art no. 12434 / 12457 Fil-Tec's M/Jumbo patented magnetic-core creates consistent delivery throughout the entire bobbin.
No more interruptions for tension adjustments as your bobbin gets smaller. Magnetic core prevents backlash or over spin & eliminates the need for backlash springs. Each bobbin has 135 yards of continuous polyester filament thread. Contains 100 per box. 

Available in color black and white

Guidelines for Underthread use: For standard length stitches the general rule for underthread requirement is around 3 m per 1000 stitches.
Upper thread: You can expect approximately 5 m per 1000 stitches. 
Correct thread tension: A perfectly tensioned embroidery with standard length stitches should have around one third of the underthread visible on the stitches underneath!