SINGER 14T967DC-WORKBOOK QUANTUMLOCK - Manual (Page 212)

Thread Middle Cover needle with regular
overlock thread.
1. Raise the Presser Foot to release the
tension disks. Thread the Cover
Stitch Middle/Chain Stitch needle as
illustrated 1-9.
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.
4. While holding the thread, firmly pull the thread between the tension disks.
Triple Cover Stitch page 10