Mavita, the wooden spools I have for my National Two Spool (which is a treadle) are much deeper than a regular spool of thread. I've never checked out how many yards of thread the spools (2 or 3) that I have will hold. In this particular instance, I don't really care -- this machine is an "heirloom" machine as far as I am concerned because it was owned by my husband's great-grandmother. It's quite old (although I really don't know how old) and it will eventually belong to my son. It's "on loan" to me right now! LOL!
Jeanette