If you can find these made with cotton on a hollow plastic tube, you have most likely found a source of inexpensive tubes. Test the tubes before going into production: they must be able to melt to a collar and also be soft enough not to crack when stressed in a cast.
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The Global FlyFisher has been online since the mid-90's and has been free to access for everybody since day one – and will stay free for as long as I run it.
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See more details about what you can do to help in this blog post.