SINGER 14T967DC-WORKBOOK QUANTUMLOCK - Manual (Page 86)

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 .
3. Thread the top cover thread guide by pulling the thread towards the left until
it slips under the guide. Then pull the thread along the right side of the
button as illustrated.
Three-Thread Flatlock (narrow) page 10