I have the Espire and it works fine as long as the needle is in the fully up position (doesn't matter if you are using 3.5 or 6.5). One time I raised the needle using the hand wheel and then tried to thread it and there was a clunk sound. I realized right away what I had done (probably hadn't raised the needle all the way to the top) so I lowered and raised the needle using the "needle up/down" button and the threader worked fine again.