Certain bobbins fit certain boat shuttles. Look at the cavities in your shuttles to determine which is the right type of bobbin to use. When I was learning to weave I heard about this but didn’t think it was important. Then when I was demonstrating fast weaving with the wrong bobbin I was embarrassed because the weft thread kept jerking. I learned my lesson that day. This is from Weaving for Beginners on page 94. I hope this saves other weavers from frustration!
The cavity in the shuttle where the spindle is mounted has either squared-off corners or oval, rounded corners. You need to fit the bobbin to the cavity in your shuttle or the thread will jerk or jam as you are weaving. Squared-off corners of the cavity are for bobbins with flanges at the ends—similar to those on the ends of spools of sewing thread. See Figure 223a. In a round-cornered cavity, use bobbins with extensions sticking out from the flanges. See Figure 223b. Bobbins with extensions are readily available and can be used in either type of shuttle. You can put a small bead or a sewing machine bobbin on the spindle at each end of the bobbin if your bobbins don’t have extensions, and your shuttle has rounded corners in the cavity. See Figure 223c.
There is more about handling boat shuttles beginning on page 111. Learn to weave without the weft thread jerking and tangling.