Plain tube and Clot Activator tube Tube info. Plain Tube is used to obtain serum specimen for clinical biochemistry, immunology and Serology Tests in clinical analysis.Serum is separated naturally from blood cells and fibrin in plain tube by physico-chemical properties. Shelf Life 24 Months Tube Material GLASS – PLASTIC Cap Color RED Cap Color invert the tube from 6-8 times and centrifuge for 5-10 minutes after blood clotting. Available Sizes