It suits various device , the pens , power bank , RDA Pen batteries the rectangle hole size : 57mm x 40mm for holding Mod Batery The Round hole Φ 26mm for RDA pen battery the hole Φ15mm for pen battery , the hole Φ12mm for pen battery the size suits most devices , you need such a cup holder in your car Handmade Wooden Car Holder for RDA RTA Atty or Battery Pen or Power Bank Stand Holder Traffic car Holder