I have the Sapphire 830 that I bought when it first came out. I spent so much on 1/4 inch feet trying to get it right.
Then I discoved it has a 1/4 in setting, duh. Now I just use the regular foot and adjust the needle for a scant.
I use coats thread and it works fine but dont buy it at Walmart.
I use the spring foot cause it is easy to see where to go.