Wow, this is even more info than you guys gave me a few weeks ago for the same problem. I still don't have my 401 going because I lost a very small screw that holds the entire top thread tension assembly together. Miriam, the part you sent me looks to be the correct one and I was ready to put it all together and found that the ***** cat had tipped over the cup with all the tiny pieces in it, and the screw is gone. I suspect I vacuumed it up, not realizing that the cup was upended. So now to search for a screw. I truly want to use this machine so will do whatever to get it together correctly, and all the support here has been a lifesaver.