Upgrades include everything you need to add a new size to your wheel base:
The 16 oz setup fits the following wheel models: MACH III, Firefly, Echo and Hopper.
You can order your wheel with your favorite size(s), and add the 16 oz upgrade to your collection when you are ready.
This is a great size bobbin. The 16oz is the same height as the 8oz bobbins, but twice as wide. This means you can use all your 8oz bobbins with the bigger flyer head too. :-D