Test tubes with screw cap Test tubes with screw cap are available with either sterile or non sterile. Available in following Specifications. -21431 Test tube 16x120 mm 15 ml cylindrical in polystyrene light blue screw cap -21432 Test tube 16x120 mm 15 ml cylindrical in polystyrene red screw cap, sterile -21433 Test tube 16x120 mm 15 ml cylindrical in polystyrene red screw cap, individually wrapped, sterile