From my understanding, the insert is so that it will sit on a spool pin and not spin loosely. It actually should be on a holder and not directly on the vertical spool pin on the machine. I measured some of the machines, including a White 43, and none are over 2 inches. The cone thread holder like
https://www.sewingpartsonline.com/do...r-hemline.aspx or
https://www.amazon.com/Dritz-921-Thr.../dp/B0019KDYL2 would have a pin that is 4 inches tall. I'm wondering
if the insert is soft enough that it would fit on the taller spool pin and hold it sturdy. There are several DIY ways to make a cone thread holder.
For the type of thread that you are using (cross wound), it should not sit on the top of your White 77. It should be sitting behind or beside the machine and have some type of guide at the top of the holder to get the thread to the top of the machine. Preferably the thread would go through a guide on the machine so that it follows the same path as if you were using stack wound thread.
With that size of thread, one should use a larger needle, probably size 16 or 18. They also make machine needles (top stitching) that have a larger eye so that the thread goes through smoothly. I see from your profile and one of the other posts that you are wanting to sew heavier fabric and leather. I don't know what size leather needles come in. I would suggest that if you are using the larger needle and especially a leather needle, to turn the hand wheel by hand to make sure that the needle clears the needle hole. I would also suggest that you sew a little slower than if you were sewing some of the thinner fabrics.
Janey - Neat people never make the exciting discoveries I do.
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