Features :The groove of the holes is not required so that enable to use for any type of holes. Sizes :M5 inside dia Φ 2.0 、outisd diaΦ 3.6. :M6 inside diaΦ2.5 、outside diaΦ4.4. :M8 inside diaΦ3.5 、outside diaΦ5.9. Material :SUS04-CSP Use :A retainer for various mechianism and resin.