I do a lot of machine embroider and have lots of thread
for that as well as quilting thread. I buy the plastic boxes
in the toy dept that are meant for hot wheels cars. Even the longer embroidery thread fits in them. I use bobbin boxes for bobbins but they would fit in the slot with the thread. These boxes are opaque and sturdy and each will hold 48 spools. Get them at Walmart for about $7.00. cheaper than going to the fabric store!