I'm using 29x3 needles and I've tried size 69 thread and size 92. I don't use 92 in the bobbin though. The shuttle works fine in my 29k-71 singer, I'll order a new one and see. The thread slips by the spring on the shuttle carrier easily. It's almost like the spring doesn't keep the shuttle against the wall tight enough to pick up the loop. The wall is worn, but I didn't think it was that bad. I'll mess with the timing some more and see.