I am thinking the same thing as dunster, one bobbin in 10 days your lucky.😳 I use glide polyester thread, 40 wt, I fill my own bobbins and find polyester thread last longer then when I was using cotton in a bobbin. But I still use up to 5 a day at times, obviously depends on how much time I get to sew and my stitch I am using. I would say on average I use 2 bobbins a day on a weekend day when I am off work and can sew to my hearts content.