SINGER 14T967DC-WORKBOOK QUANTUMLOCK - Manual (Page 119)

7. Thread the hole in the Upper Looper from front to back . Pull about 4
inches of thread through the looper and place to the back of the
throat plate.
Thread Lower Looper with regular overlock thread.
1. Raise the Presser Foot to release the Tension disks. Thread the Lower
Looper as illustrated 1-10.
2. Pass thread from back to the front through the thread guide .
Four-Thread Ultra-Stretch Mock Safety Stitch page 9