Chalkzies Chalkboard Magnet Jar Lid Labels (Regular Mouth 24-Pack) (24) Regular Mouth Chalkboard Magnet Jar Lid Labels. Strong flexible magnet on the back and a chalkboard surface on the front. Easily put on or taken off in seconds. Reusable over and over again. Fits: Regular Mouth (Steel) Canning Jar Lids. Magnet will not stick to plastic lids. This is the best way to label your canning jars!