This terahertz bracelet uses 8mm beads, with three green beads made of green onyx. The effects of terahertz are widely documented online, so I'll omit them here, but I personally attest to their effectiveness and wear the bracelet while sleeping. The Antaron rubber used to string the bracelet stretches slightly. I will adjust the size, so please specify the "number of beads" based on the following information (maximum 27 beads). ＜Inner Circumference Reference for 8mm Bead Bracelets＞ 21 beads = 14.3cm 22 beads = 15.1cm 23 beads = 15.9cm 24 beads = 16.7cm 25 beads = 17.5cm 26 beads = 18.3cm 27 beads = 19.1cm