These are 5″ (12 cm) and 8″ (20 cm) needle gauges. All are made of durable plastic.
In addition, the Swatch/needle gauge 5.5" square gauge has conversion charts and yarn standards tables for reference. Simply place the tool on your swatch and count how many stitches/rows fit inside the cut-outs (along the bottom for stitch gauge and up the side for the row gauge.) The tool is double-sided for US/knitting vs. metric/crochet differentiation. Made in the USA. Measures approximately 5.5" (14cm) square.