Welcome to the Quilting Board!
they work wonders with a horizontal spool shaft---------a must have if you're working with invisible thread. You push the net thru the center, bring it up around the spool like slipping on a sock. Put the spool on the horizontal shaft with the open ends to the left. Work wonders
However, if you have a vertical shaft like I do, the thread sock/net whatever won't work.
Bad Spellers of the World
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