Vacuum Blood Collection Tube (Yellow cap) Tube material: glass or plastic Volume of blood draw (ml): 1~10ml Tube Spec.(mm):12/13*75,12/13*100,15/16*100,15*120mm Tube with yellow cap, called Gel & Clot Activator Tube , with additive of Gel & Clot Activator, used for for biochemistry and immunology tests, There is gel inside the tube at the bottom. After centrifugation, the gel can separate the serum from the blood cells.