Plastic Disk For Brush Wheel for 4.5 mm machines - This is a plastic disk wheel (also called a brush cover) that fits over the brush wheel on the Artisan 245, Studio Singer Silver Reed standard gauge 4.5 mm  knitting machines. 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. These are inexpensive items and having a set of extra plastic disks is a good idea. You just have to remember where you put the extra set! ;o)