A cast on rag (though not really a rag), is a strip of yarn fabric used to hang the cast on comb or other weights, to save time, without distorting the first row of knitting or cast on.
It not only saves yarn used to knit waste yarn, but it saves time!
These can be purchased for a bulky gauge (9 mm) knitting machines,
mid-gauge (6.5) or standard gauge (4.5 mm) knitting machines.
Colors vary.