When I bought my 401 at an estate sale, I asked if it worked. They plugged it in and used a very thin piece of see through cotton. I pulled my "heavy denim test kit" out of my purse and told them to let me try it. It sewed like a knife going through melted butter and was purring like a kitten. I paid $150.00 for it and do not regret it one bit. It's in a desk cabinet. Not what I was looking for but. I can put it down and use my other machine on top. I have a board the length and width of the cabinet to balance the weight of my other machine. Posting this because if you go to any sales where there is a machine to try out, take a "denim test kit" with you. Mine is just a 6x6" square of denim. If it passes the denim test you should be good to go. I did make sure first see that the stitching for the fabric and the bobbin case (free of lint) were in good shape before. Light denim shows light and dark thread. Love that machine. DH uses it too.