maybe this text can help you (for me, the question in new too).
Thick Threads -- Large Spring and Tension Plates
If you have an AVL shuttle with two tension springs and plates to hold the yarn, then you may use it in the same way as the standard AVL shuttle. Screwing in the tensioning screws on the shuttle's side will increase tension on the filling yarn and loosening the screws will decrease tension. To thread the shuttle, simply pull the fill thread off the end of the bobbin. Use a small hook (perhaps a crochet hook) to get the thread out the side hole.