My Viking Sapphire 830 works best with Coats and Clarks, the kind with the pull up top that holds the thread end.
I tried Connecting Threads but it did not like it.
C&C is cheaper also.
When I took my machine in for servicing I found out the plastic caps that sit on top of the thread, well Ive been using them upside down, the long end goes inside the thread spool. DUH.