Did you know, you can use your bobbin winder on the sewing machine to wind more thread on the regular size spool?
It's always cheaper to buy anything in bulk or in larger amounts.
When I buy large size of Sulky, Aurifil, Kingtut or Superior threads, yes, I always win in price, but it's not not always convenient having a big spool, especially when you travelling, go for a class or guild meetings.
It also applies to serger or coverlock, when I need 4 spools of the same color at a time, but I have only one available (or 2-3, still not enough!), you would like this tip to know how to rewind it.
Just buy sticky Velcro circles
and punch the whole in the center.
Attach one to the bobbin and one to the empty spool.
Just hold the top of the spool, when winding, to prevent it from wobbling.