Plastic Disk For Brush Wheel - This is a plastic wheel (also called a brush cover) that fits over the brush wheel on the Artisan 70d or 70D+ knitting machine. The plastic disk or brush cover helps the brush wheels push the yarn back against the sinker posts. If there are nicks in the plastic wheel, the knitting can be snagged giving uneven stitches as well as dropped or unknitted stitches. Sometimes the brush cover gets bent and can be bent back somewhat into shape. If the edge of the plastic wheel gets ragged and chipped, it is time to replace them. The quality of your knitting will be the first indication. The hole in the middle of the plastic disk is larger than the brush covers found on other knitting machines. These are inexpensive items and having a set of extras is a good idea. You just have to remember where you put the extra set! ;o)