The 8-425 pp cap produced by aijiren has only two colors, white and black, with closed -The top cap is used for storage and has a 5.5 center hole to facilitate automatic sampling needle in and out. The 9mm 2ml Screw Vial has a short thread, which makes the 9mm 2ml Screw Vial have a longer neck compared to the 8mm and 10mm hplc vial.