I had a Delta Rotary on which I could not figure out how to thread. I tried many different ways, but nothing worked. Then my young sewing machine guy sold me an Eldridge Two Spool. Lo and behold, it had the same threading, and a book came with it. On those machines, the thread makes a complete turn around the tension disks. The thread actually crosses over it self twice on its path to the needle. Who would-a thought? ? ?