I use the empty bolts from where ever, and cut them in half (width wise) so I have my mini bolts and then wind on
them. I do however go one step further and measure my bigger pieces ( just a quick measure) so if I am looking for a piece for a backing, and lets say I need a 4 yard piece, I can tell if a piece will work. I just use a straight pin and a scrap piece of paper and say 6 yards, and if I take anything off, just do the math on that paper.... works for me.